?Silberschatz,Korth and Sudarshan4.1Database System Concepts
Chapter 4,SQL
? Background
? Basic Structure
? Set Operations
? Aggregate Functions
? Null Values
? Nested Subqueries
? Derived Relations
? Views
? Modification of the Database
? Joined Relations
? Data Definition Language
? Embedded SQL,ODBC and JDBC
?Silberschatz,Korth and Sudarshan4.2Database System Concepts
Background
? In 1986,ANSI and ISO published an SQL standard,
called SQL-86
? In 1989,ANSI published an extended standard for SQL,
called SQL-89
? SQL-92 and SQL-1999(SQL3)
? The SQL language has several parts:
? Data-definition language (DDL)
? Interactive data-manipulation language (DML)
? View definition
? Transaction control
? Embedded SQL and dynamic SQL
? Integrity
? Authorization
?Silberschatz,Korth and Sudarshan4.3Database System Concepts
Basic Structure
? A typical SQL query has the form:
select A1,A2,...,An
from r1,r2,...,rm
where P
? Ais represent attributes
? ris represent relations
? P is a predicate.
? This query is equivalent to the relational algebra
expression.
?A1,A2,...,An(?P (r1 x r2 x,.,x rm))
? The result of an SQL query is a relation.
?Silberschatz,Korth and Sudarshan4.4Database System Concepts
The select Clause
? The select clause list the attributes desired in the result
of a query
? corresponds to the projection operation of the
relational algebra
? E.g,find the names of all branches in the loan relation
select branch-name
from loan
? In the,pure” relational algebra syntax,the query would
be,
?branch-name(loan)
?Silberschatz,Korth and Sudarshan4.5Database System Concepts
The select Clause (Cont.)
? SQL allows duplicates in relations as well as in
query results.
? To force the elimination of duplicates,insert the
keyword distinct after select.
? Find the names of all branches in the loan
relations,and remove duplicates
select distinct branch-name
from loan
? The keyword all specifies that duplicates not be
removed.
select all branch-name
from loan
?Silberschatz,Korth and Sudarshan4.6Database System Concepts
The select Clause (Cont.)
? An asterisk in the select clause denotes,all attributes”
select *
from loan
? The select clause can contain arithmetic expressions
involving the operation,+,–,?,and /,and operating
on constants or attributes of tuples.
? The query,
select loan-number,branch-name,amount ? 100
from loan
would return a relation which is the same as the loan
relations,except that the attribute amount is multiplied
by 100.
?Silberschatz,Korth and Sudarshan4.7Database System Concepts
The where Clause
? The where clause specifies conditions that the result
must satisfy
? corresponds to the selection predicate of the
relational algebra,
? To find all loan number for loans made at the
Perryridge branch with loan amounts greater than
$1200.
select loan-number
from loan
where branch-name = ?Perryridge? and
amount > 1200
? Comparison results can be combined using the logical
connectives and,or,and not.
?Silberschatz,Korth and Sudarshan4.8Database System Concepts
The where Clause (Cont.)
? SQL includes a between comparison operator
? E.g,Find the loan number of those loans with loan
amounts between $90,000 and $100,000 (that is,
?$90,000 and ?$100,000)
select loan-number
from loan
where amount between 90000 and 100000
?Silberschatz,Korth and Sudarshan4.9Database System Concepts
The from Clause
? The from clause lists the relations involved in the query
? corresponds to the Cartesian product operation of the
relational algebra.
? Find the Cartesian product borrower x loan
select ?
from borrower,loan
? Find the name,loan number and loan amount of all
customers having a loan at the Perryridge branch.
select customer-name,borrower.loan-number,amount
from borrower,loan
where borrower.loan-number = loan.loan-number and
branch-name = ?Perryridge?
?Silberschatz,Korth and Sudarshan4.10Database System Concepts
The Rename Operation
? The SQL allows renaming relations and attributes using
the as clause:
old-name as new-name
? Find the name,loan number and loan amount of all
customers; rename the column name loan-number as
loan-id.
select customer-name,borrower.loan-number as
loan-id,amount
from borrower,loan
where borrower.loan-number = loan.loan-number
?Silberschatz,Korth and Sudarshan4.11Database System Concepts
Tuple Variables
? Tuple variables are defined in the from clause via the
use of the as clause.
? Find the customer names and their loan numbers for
all customers having a loan at some branch.
select distinct T.branch-name
from branch as T,branch as S
where T.assets > S.assets and S.branch-city = ?Brooklyn?
? Find the names of all branches that have greater
assets than some branch located in Brooklyn.
select customer-name,T.loan-number,S.amount
from borrower as T,loan as S
where T.loan-number = S.loan-number
?Silberschatz,Korth and Sudarshan4.12Database System Concepts
String Operations
? SQL includes a string-matching operator for comparisons on
character strings,Patterns are described using two special
characters:
? percent (%),The % character matches any substring.
? underscore (_),The _ character matches any character.
? Find the names of all customers whose street includes the
substring,Main”.
select customer-name
from customer
where customer-street like ‘%Main%’
? SQL supports a variety of string operations such as
? concatenation (using,||”)
? converting from upper to lower case (and vice versa)
? finding string length,extracting substrings,etc.
?Silberschatz,Korth and Sudarshan4.13Database System Concepts
Ordering the Display of Tuples
? List in alphabetic order the names of all customers having a
loan in Perryridge branch
select distinct customer-name
from borrower,loan
where borrower loan-number = loan.loan-number and
branch-name = ‘Perryridge’
order by customer-name
? We may specify desc for descending order or asc for
ascending order,for each attribute; ascending order is the
default.
? E.g,order by customer-name desc
?Silberschatz,Korth and Sudarshan4.14Database System Concepts
Set Operations
? The set operations union,intersect,and except operate on
relations and correspond to the relational algebra operations
????????
? Each of the above operations automatically eliminates
duplicates; to retain all duplicates use the corresponding
multiset versions union all,intersect all and except all.
Suppose a tuple occurs m times in r and n times in s,then,it
occurs:
? m + n times in r union all s
? min(m,n) times in r intersect all s
? max(0,m – n) times in r except all s
?Silberschatz,Korth and Sudarshan4.15Database System Concepts
Set Operations
? Find all customers who have a loan,an account,or both:
(select customer-name from depositor)
except
(select customer-name from borrower)
(select customer-name from depositor)
intersect
(select customer-name from borrower)
? Find all customers who have an account but no loan.
(select customer-name from depositor)
union
(select customer-name from borrower)
? Find all customers who have both a loan and an account.
?Silberschatz,Korth and Sudarshan4.16Database System Concepts
Aggregate Functions
? These functions operate on the multiset of values of a
column of a relation,and return a value
avg,average value
min,minimum value
max,maximum value
sum,sum of values
count,number of values
?Silberschatz,Korth and Sudarshan4.17Database System Concepts
Aggregate Functions (Cont.)
? Find the average account balance at the Perryridge branch.
? Find the number of depositors in the bank.
? Find the number of tuples in the customer relation.
select avg (balance)
from account
where branch-name = ?Perryridge?
select count (*)
from customer
select count (distinct customer-name)
from depositor
?Silberschatz,Korth and Sudarshan4.18Database System Concepts
Aggregate Functions – Group By
? Find the number of depositors for each branch.
Note,Attributes in select clause outside of aggregate
functions must appear in group by list
select branch-name,count (distinct customer-name)
from depositor,account
where depositor.account-number
= account.account-number
group by branch-name
?Silberschatz,Korth and Sudarshan4.19Database System Concepts
Aggregate Functions – Having Clause
? Find the names of all branches where the average
account balance is more than $1,200.
Note,predicates in the having clause are applied after
the formation of groups whereas predicates in the
where clause are applied before forming groups
select branch-name,avg (balance)
from account
group by branch-name
having avg (balance) > 1200
?Silberschatz,Korth and Sudarshan4.20Database System Concepts
Null Values
? It is possible for tuples to have a null value,denoted by null,
for some of their attributes
? null signifies an unknown value or that a value does not
exist.
? The predicate is null can be used to check for null values.
? E.g,Find all loan number which appear in the loan
relation with null values for amount.
select loan-number
from loan
where amount is null
? The result of any arithmetic expression involving null is null
? E.g,5 + null returns null
?Silberschatz,Korth and Sudarshan4.21Database System Concepts
Null Values and Three Valued Logic
? Any comparison with null returns unknown
? E.g,5 < null or null <> null or null = null
? Three-valued logic using the truth value unknown:
? OR,(unknown or true) = true,(unknown or false) =
unknown,(unknown or unknown) = unknown
? AND,(true and unknown) = unknown,(false and
unknown) = false,(unknown and unknown) = unknown
? NOT,(not unknown) = unknown
?,P is unknown” evaluates to true if predicate P
evaluates to unknown
?Silberschatz,Korth and Sudarshan4.22Database System Concepts
Null Values and Aggregates
? Total all loan amounts
select sum (amount)
from loan
? Above statement ignores null amounts
? result is null if there is no non-null amount
? All aggregate operations except count(*) ignore
tuples with null values on the aggregated attributes.
?Silberschatz,Korth and Sudarshan4.23Database System Concepts
Nested Subqueries
? SQL provides a mechanism for the nesting of
subqueries.
? A subquery is a select-from-where expression that is
nested within another query.
? A common use of subqueries is to perform tests for
set membership,set comparisons,and set cardinality.
?Silberschatz,Korth and Sudarshan4.24Database System Concepts
Example Query
? Find all customers who have both an account and a
loan at the bank.
? Find all customers who have a loan at the bank but
do not have an account at the bank
select distinct customer-name
from borrower
where customer-name not in (select customer-name
from depositor)
select distinct customer-name
from borrower
where customer-name in (select customer-name
from depositor)
?Silberschatz,Korth and Sudarshan4.25Database System Concepts
Example Query
? Find all customers who have both an account and a
loan at the Perryridge branch
select distinct customer-name
from borrower,loan
where borrower.loan-number = loan.loan-number and
branch-name =,Perryridge” and
(branch-name,customer-name) in
(select branch-name,customer-name
from depositor,account
where depositor.account-number =
account.account-number)
?Silberschatz,Korth and Sudarshan4.26Database System Concepts
Set Comparison
? Find all branches that have greater assets than some
branch located in Brooklyn.
? Same query using > some clause (至少比一个要大 )
select branch-name
from branch
where assets > some
(select assets
from branch
where branch-city = ‘Brooklyn’)
select distinct T.branch-name
from branch as T,branch as S
where T.assets > S.assets and
S.branch-city = ‘Brooklyn’
?Silberschatz,Korth and Sudarshan4.27Database System Concepts
Example Query
? Find the names of all branches that have greater
assets than all branches located in Brooklyn.
select branch-name
from branch
where assets > all
(select assets
from branch
where branch-city = ?Brooklyn?)
(大于所有的 )
?Silberschatz,Korth and Sudarshan4.28Database System Concepts
Example Query
? Find all customers who have an account at all branches
located in Brooklyn.
select distinct S.customer-name
from depositor as S
where not exists (
(select branch-name
from branch
where branch-city = ?Brooklyn?)
except
(select R.branch-name
from depositor as T,account as R
where T.account-number = R.account-number and
S.customer-name = T.customer-name))
?Silberschatz,Korth and Sudarshan4.29Database System Concepts
Test for Absence of Duplicate Tuples
? The unique construct tests whether a subquery has any
duplicate tuples in its result.
? Find all customers who have at most one account at the
Perryridge branch.
select T.customer-name
from depositor as T
where unique (
select R.customer-name
from account,depositor as R
where T.customer-name = R.customer-name and
R.account-number = account.account-number and
account.branch-name = ?Perryridge?)
? (Schema used in this example)
?Silberschatz,Korth and Sudarshan4.30Database System Concepts
Example Query
? Find all customers who have at least two accounts at the
Perryridge branch,
select distinct T.customer-name
from depositor T
where not unique (
select R.customer-name
from account,depositor as R
where T.customer-name = R.customer-name
and
R.account-number = account.account-number
and
account.branch-name = ‘Perryridge’)
?(Schema used in this example)
?Silberschatz,Korth and Sudarshan4.31Database System Concepts
Views
? Provide a mechanism to hide certain data from the view of
certain users,To create a view we use the command:
create view v as <query expression>
where:
?<query expression> is any legal expression
?The view name is represented by v
?Silberschatz,Korth and Sudarshan4.32Database System Concepts
Example Queries
? A view consisting of branches and their customers
? Find all customers of the Perryridge branch
create view all-customer as
(select branch-name,customer-name
from depositor,account
where depositor.account-number = account.account-number)
union
(select branch-name,customer-name
from borrower,loan
where borrower.loan-number = loan.loan-number)
select customer-name
from all-customer
where branch-name = ?Perryridge?
?Silberschatz,Korth and Sudarshan4.33Database System Concepts
Derived Relations
? Find the average account balance of those branches where the
average account balance is greater than $1200.
select branch-name,avg-balance
from (select branch-name,avg (balance)
from account
group by branch-name)
as result (branch-name,avg-balance)
where avg-balance > 1200
Note that we do not need to use the having clause,since we
compute the temporary (view) relation result in the from clause,
and the attributes of result can be used directly in the where
clause.
?Silberschatz,Korth and Sudarshan4.34Database System Concepts
With Clause
? With clause allows views to be defined locally to a query,rather
than globally,Analogous to procedures in a programming
language.
? Find all accounts with the maximum balance
with max-balance(value) as
select max (balance)
from account
select account-number
from account,max-balance
where account.balance = max-balance.value
?Silberschatz,Korth and Sudarshan4.35Database System Concepts
Complex Query using With Clause
? Find all branches where the total account deposit is greater than
the average of the total account deposits at all branches.
with branch-total (branch-name,value) as
select branch-name,sum (balance)
from account
group by branch-name
with branch-total-avg(value) as
select avg (value)
from branch-total
select branch-name
from branch-total,branch-total-avg
where branch-total.value >= branch-total-avg.value
?Silberschatz,Korth and Sudarshan4.36Database System Concepts
Modification of the Database – Deletion
? Delete all account records at the Perryridge branch
delete from account
where branch-name = ‘Perryridge’
? Delete all accounts at every branch located in Needham city.
delete from account
where branch-name in (select branch-name
from branch
where branch-city = ‘Needham’)
delete from depositor
where account-number in
(select account-number
from branch,account
where branch-city = ‘Needham’
and branch.branch-name = account.branch-name)
? (Schema used in this example)
?Silberschatz,Korth and Sudarshan4.37Database System Concepts
Example Query
? Delete the record of all accounts with balances below the
average at the bank.
delete from account
where balance < (select avg (balance)
from account)
? Problem,as we delete tuples from deposit,the average balance
changes
? Solution used in SQL:
1,First,compute avg balance and find all tuples to delete
2,Next,delete all tuples found above (without recomputing avg or
retesting the tuples)
?Silberschatz,Korth and Sudarshan4.38Database System Concepts
Modification of the Database – Insertion
? Add a new tuple to account
insert into account
values (?A-9732?,?Perryridge?,1200)
or equivalently
insert into account (branch-name,balance,account-number)
values (?Perryridge?,1200,?A-9732?)
? Add a new tuple to account with balance set to null
insert into account
values (?A-777?,?Perryridge?,null)
?Silberschatz,Korth and Sudarshan4.39Database System Concepts
Modification of the Database – Insertion
? Provide as a gift for all loan customers of the Perryridge branch,a
$200 savings account,Let the loan number serve as the account
number for the new savings account
insert into account
select loan-number,branch-name,200
from loan
where branch-name = ?Perryridge?
insert into depositor
select customer-name,loan-number
from loan,borrower
where branch-name = ?Perryridge?
and loan.account-number = borrower.account-number
? The select from where statement is fully evaluated before any of its
results are inserted into the relation (otherwise queries like
insert into table1 select * from table1
would cause problems
?Silberschatz,Korth and Sudarshan4.40Database System Concepts
Modification of the Database – Updates
? Increase all accounts with balances over $10,000 by 6%,all
other accounts receive 5%.
? Write two update statements:
update account
set balance = balance ? 1.06
where balance > 10000
update account
set balance = balance ? 1.05
where balance ? 10000
? The order is important
? Can be done better using the case statement (next slide)
?Silberschatz,Korth and Sudarshan4.41Database System Concepts
Case Statement for Conditional Updates
? Same query as before,Increase all accounts with balances over
$10,000 by 6%,all other accounts receive 5%.
update account
set balance = case
when balance <= 10000 then balance *1.05
else balance * 1.06
end
?Silberschatz,Korth and Sudarshan4.42Database System Concepts
Update of a View
? Create a view of all loan data in loan relation,hiding the amount
attribute
create view branch-loan as
select branch-name,loan-number
from loan
? Add a new tuple to branch-loan
insert into branch-loan
values (?Perryridge?,?L-307?)
This insertion must be represented by the insertion of the tuple
(?L-307?,?Perryridge?,null)
into the loan relation
? Updates on more complex views are difficult or impossible to
translate,and hence are disallowed,
? Most SQL implementations allow updates only on simple views
(without aggregates) defined on a single relation
?Silberschatz,Korth and Sudarshan4.43Database System Concepts
Transactions
? A transaction is a sequence of queries and update statements executed
as a single unit
? Transactions are started implicitly and terminated by one of
? commit work,makes all updates of the transaction permanent in the
database
? rollback work,undoes all updates performed by the transaction,
? Motivating example
? Transfer of money from one account to another involves two steps:
? deduct from one account and credit to another
? If one steps succeeds and the other fails,database is in an inconsistent state
? Therefore,either both steps should succeed or neither should
? If any step of a transaction fails,all work done by the transaction can be
undone by rollback work,
? Rollback of incomplete transactions is done automatically,in case of
system failures
?Silberschatz,Korth and Sudarshan4.44Database System Concepts
Transactions (Cont.)
? In most database systems,each SQL statement that executes
successfully is automatically committed,
? Each transaction would then consist of only a single statement
? Automatic commit can usually be turned off,allowing multi-
statement transactions,but how to do so depends on the database
system
? Another option in SQL:1999,enclose statements within
begin atomic
…
end
?Silberschatz,Korth and Sudarshan4.45Database System Concepts
Joined Relations
? Join operations take two relations and return as a result another
relation.
? These additional operations are typically used as subquery
expressions in the from clause
? Join condition – defines which tuples in the two relations match,
and what attributes are present in the result of the join.
? Join type – defines how tuples in each relation that do not match
any tuple in the other relation (based on the join condition) are
treated.
Join Types
inner join
left outer join
right outer join
full outer join
Join Conditions
natural
on <predicate>
using (A1,A2,...,An)
?Silberschatz,Korth and Sudarshan4.46Database System Concepts
Joined Relations – Datasets for Examples
? Relation loan
? Relation borrower
customer-name loan-number
Jones
Smith
Hayes
L-170
L-230
L-155
amount
3000
4000
1700
branch-name
Downtown
Redwood
Perryridge
loan-number
L-170
L-230
L-260
? Note,borrower information missing for L-260 and loan
information missing for L-155
?Silberschatz,Korth and Sudarshan4.47Database System Concepts
Joined Relations – Examples
? loan inner join borrower on
loan.loan-number = borrower.loan-number
? loan left outer join borrower on
loan.loan-number = borrower.loan-number
branch-name amount
Downtown
Redwood
3000
4000
customer-name loan-number
Jones
Smith
L-170
L-230
loan-number
L-170
L-230
branch-name amount
Downtown
Redwood
Perryridge
3000
4000
1700
customer-name loan-number
Jones
Smith
null
L-170
L-230
null
loan-number
L-170
L-230
L-260
?Silberschatz,Korth and Sudarshan4.48Database System Concepts
Joined Relations – Examples
? loan natural inner join borrower
? loan natural right outer join borrower
branch-name amount
Downtown
Redwood
3000
4000
customer-name
Jones
Smith
loan-number
L-170
L-230
branch-name amount
Downtown
Redwood
null
3000
4000
null
customer-name
Jones
Smith
Hayes
loan-number
L-170
L-230
L-155
?Silberschatz,Korth and Sudarshan4.49Database System Concepts
Joined Relations – Examples
? loan full outer join borrower using (loan-number)
? Find all customers who have either an account or a loan (but
not both) at the bank.
branch-name amount
Downtown
Redwood
Perryridge
null
3000
4000
1700
null
customer-name
Jones
Smith
null
Hayes
loan-number
L-170
L-230
L-260
L-155
select customer-name
from (depositor natural full outer join borrower)
where account-number is null or loan-number is null
?Silberschatz,Korth and Sudarshan4.50Database System Concepts
Data Definition Language (DDL)
? The schema for each relation.
? The domain of values associated with each attribute.
? Integrity constraints
? The set of indices to be maintained for each relations.
? Security and authorization information for each relation.
? The physical storage structure of each relation on disk.
Allows the specification of not only a set of relations but also
information about each relation,including:
?Silberschatz,Korth and Sudarshan4.51Database System Concepts
Domain Types in SQL
? char(n),Fixed length character string,with user-specified length n.
? varchar(n),Variable length character strings,with user-specified maximum
length n.
? int,Integer (a finite subset of the integers that is machine-dependent).
? smallint,Small integer (a machine-dependent subset of the integer
domain type).
? numeric(p,d),Fixed point number,with user-specified precision of p digits,
with n digits to the right of decimal point,
? real,double precision,Floating point and double-precision floating point
numbers,with machine-dependent precision.
? float(n),Floating point number,with user-specified precision of at least n
digits.
? Null values are allowed in all the domain types,Declaring an attribute to be
not null prohibits null values for that attribute.
? create domain construct in SQL-92 creates user-defined domain types
create domain person-name char(20) not null
?Silberschatz,Korth and Sudarshan4.52Database System Concepts
Date/Time Types in SQL (Cont.)
? date,Dates,containing a (4 digit) year,month and date
? E.g,date ?2001-7-27?
? time,Time of day,in hours,minutes and seconds.
? E.g,time ?09:00:30? time ?09:00:30.75?
? timestamp,date plus time of day
? E.g,timestamp ?2001-7-27 09:00:30.75?
? Interval,period of time
? E.g,Interval ?1? day
? Subtracting a date/time/timestamp value from another gives an interval value
? Interval values can be added to date/time/timestamp values
? Can extract values of individual fields from date/time/timestamp
? E.g,extract (year from r.starttime)
? Can cast string types to date/time/timestamp
? E.g,cast <string-valued-expression> as date
?Silberschatz,Korth and Sudarshan4.53Database System Concepts
Create Table Construct
? An SQL relation is defined using the create table
command:
create table r (A1 D1,A2 D2,...,An Dn,
(integrity-constraint1),
...,
(integrity-constraintk))
? r is the name of the relation
? each Ai is an attribute name in the schema of relation r
? Di is the data type of values in the domain of attribute Ai
? Example:
create table branch
(branch-name char(15) not null,
branch-city char(30),
assets integer)
?Silberschatz,Korth and Sudarshan4.54Database System Concepts
Integrity Constraints in Create Table
? not null
? primary key (A1,...,An)
? check (P),where P is a predicate
Example,Declare branch-name as the primary key for
branch and ensure that the values of assets are non-
negative.
create table branch
(branch-namechar(15),
branch-city char(30)
assets integer,
primary key (branch-name),
check (assets >= 0))
primary key declaration on an attribute automatically
ensures not null in SQL-92 onwards,needs to be
explicitly stated in SQL-89
?Silberschatz,Korth and Sudarshan4.55Database System Concepts
Drop and Alter Table Constructs
? The drop table command deletes all information about the
dropped relation from the database.
? The alter table command is used to add attributes to an
existing relation,
alter table r add A D
where A is the name of the attribute to be added to relation r
and D is the domain of A.
? All tuples in the relation are assigned null as the value for the
new attribute,
? The alter table command can also be used to drop attributes
of a relation
alter table r drop A
where A is the name of an attribute of relation r
? Dropping of attributes not supported by many databases
?Silberschatz,Korth and Sudarshan4.56Database System Concepts
Embedded SQL
? The SQL standard defines embeddings of SQL in a variety of
programming languages such as Pascal,PL/I,Fortran,C,and
Cobol.
? A language to which SQL queries are embedded is referred to as
a host language,and the SQL structures permitted in the host
language comprise embedded SQL.
? The basic form of these languages follows that of the System R
embedding of SQL into PL/I.
? EXEC SQL statement is used to identify embedded SQL request
to the preprocessor
EXEC SQL <embedded SQL statement > END-EXEC
Note,this varies by language,E.g,the Java embedding uses
# SQL { …,} ;
?Silberschatz,Korth and Sudarshan4.57Database System Concepts
Example Query
? Specify the query in SQL and declare a cursor for it
EXEC SQL
declare c cursor for
select customer-name,customer-city
from depositor,customer,account
where depositor.customer-name = customer.customer-name
and depositor account-number = account.account-number
and account.balance >,amount
END-EXEC
From within a host language,find the names and cities of
customers with more than the variable amount dollars in some
account.
?Silberschatz,Korth and Sudarshan4.58Database System Concepts
Example Query
Query1->Close();
Query1->SQL->Clear();
Query1->SQL->Add("SELECT*from船名 WHERE编码 =:DM");
Query1->ParamByName("DM")->AsString=DBEdit1->Text;
Query1->Open();
while(!Query1->Eof)
{
DM=Query1->FieldByName("编码 ")->AsString+" ";
ZD=Query1->FieldByName("船名 ")->AsString;
LENGTH[i]=DM.Length();
Z_LENGTH[i]=(DM+ZD).Length();
ListBox1->Items->Add(DM+ZD);
i=i+1;
Query1->Next();
}
?Silberschatz,Korth and Sudarshan4.59Database System Concepts
Embedded SQL (Cont.)
? The open statement causes the query to be evaluated
EXEC SQL open c END-EXEC
? The fetch statement causes the values of one tuple in the query
result to be placed on host language variables.
EXEC SQL fetch c into,cn,:cc END-EXEC
Repeated calls to fetch get successive tuples in the query result
? A variable called SQLSTATE in the SQL communication area
(SQLCA) gets set to ?02000? to indicate no more data is available
? The close statement causes the database system to delete the
temporary relation that holds the result of the query.
EXEC SQL close c END-EXEC
Note,above details vary with language,E.g,the Java embedding
defines Java iterators to step through result tuples.
?Silberschatz,Korth and Sudarshan4.60Database System Concepts
Updates Through Cursors
? Can update tuples fetched by cursor by declaring that the cursor
is for update
declare c cursor for
select *
from account
where branch-name= ?Perryridge?
for update
? To update tuple at the current location of cursor
update account
set balance = balance + 100
where current of c
?Silberschatz,Korth and Sudarshan4.61Database System Concepts
Dynamic SQL
? Allows programs to construct and submit SQL queries at run
time.
? Example of the use of dynamic SQL from within a C program.
char * sqlprog =,update account
set balance = balance * 1.05
where account-number =?”
EXEC SQL prepare dynprog from,sqlprog;
char account [10] =,A-101”;
EXEC SQL execute dynprog using,account;
? The dynamic SQL program contains a?,which is a place holder
for a value that is provided when the SQL program is executed.
?Silberschatz,Korth and Sudarshan4.62Database System Concepts
Dynamic SQL
sSQL = "select * from 出港集装箱信息表 WHERE " + CXTJ +"
ORDER BY出港时间 ";
Query2->Close();
Query2->SQL->Clear();
Query2->SQL->Add(sSQL);
Query2->Open();
for(inti=0; i<Query2->RecordCount; i++)
{
for(int j = 0; j < ListBox3->Items->Count; j++)
Sh1.PG("Cells",i+3,j+1).PS("Value",Query2->Fields->Fields[j]-
>AsString) ;
Query2->Next();
}
?Silberschatz,Korth and Sudarshan4.63Database System Concepts
ODBC
? Open DataBase Connectivity(ODBC) standard
? standard for application program to communicate with a database
server.
? application program interface (API) to
? open a connection with a database,
? send queries and updates,
? get back results.
? Applications such as GUI,spreadsheets,etc,can use ODBC
?Silberschatz,Korth and Sudarshan4.64Database System Concepts
ODBC (Cont.)
? Each database system supporting ODBC provides a "driver" library that
must be linked with the client program.
? When client program makes an ODBC API call,the code in the library
communicates with the server to carry out the requested action,and
fetch results.
? ODBC program first allocates an SQL environment,then a database
connection handle.
? Opens database connection using SQLConnect(),Parameters for
SQLConnect:
? connection handle,
? the server to which to connect
? the user identifier,
? password
? Must also specify types of arguments:
? SQL_NTS denotes previous argument is a null-terminated string.
?Silberschatz,Korth and Sudarshan4.65Database System Concepts
ODBC Code
? int ODBCexample()
{
RETCODE error;
HENV env; /* environment */
HDBC conn; /* database connection */
SQLAllocEnv(&env);
SQLAllocConnect(env,&conn);
SQLConnect(conn,"aura.bell-labs.com",SQL_NTS,"avi",SQL_NTS,
"avipasswd",SQL_NTS);
{ …,Do actual work … }
SQLDisconnect(conn);
SQLFreeConnect(conn);
SQLFreeEnv(env);
}
?Silberschatz,Korth and Sudarshan4.66Database System Concepts
ODBC Code (Cont.)
? Program sends SQL commands to the database by using SQLExecDirect
? Result tuples are fetched using SQLFetch()
? SQLBindCol() binds C language variables to attributes of the query result
? When a tuple is fetched,its attribute values are automatically stored in
corresponding C variables.
? Arguments to SQLBindCol()
– ODBC stmt variable,attribute position in query result
– The type conversion from SQL to C,
– The address of the variable,
– For variable-length types like character arrays,
? The maximum length of the variable
? Location to store actual length when a tuple is fetched.
? Note,A negative value returned for the length field indicates null
value
? Good programming requires checking results of every function call for
errors; we have omitted most checks for brevity.
?Silberschatz,Korth and Sudarshan4.67Database System Concepts
ODBC Code (Cont.)
? Main body of program
char branchname[80];
float balance;
int lenOut1,lenOut2;
HSTMT stmt;
SQLAllocStmt(conn,&stmt);
char * sqlquery = "select branch_name,sum (balance)
from account
group by branch_name";
error = SQLExecDirect(stmt,sqlquery,SQL_NTS);
if (error == SQL_SUCCESS) {
SQLBindCol(stmt,1,SQL_C_CHAR,branchname,80,&lenOut1);
SQLBindCol(stmt,2,SQL_C_FLOAT,&balance,0,&lenOut2);
while (SQLFetch(stmt) >= SQL_SUCCESS) {
printf (" %s %g\n",branchname,balance);
}
}
SQLFreeStmt(stmt,SQL_DROP);
?Silberschatz,Korth and Sudarshan4.68Database System Concepts
More ODBC Features
? Prepared Statement
? SQL statement prepared,compiled at the database
? Can have placeholders,E.g,insert into account values(?,?,?)
? Repeatedly executed with actual values for the placeholders
? Metadata features
? finding all the relations in the database and
? finding the names and types of columns of a query result or a relation in
the database.
? By default,each SQL statement is treated as a separate transaction
that is committed automatically.
? Can turn off automatic commit on a connection
? SQLSetConnectOption(conn,SQL_AUTOCOMMIT,0)}
? transactions must then be committed or rolled back explicitly by
? SQLTransact(conn,SQL_COMMIT) or
? SQLTransact(conn,SQL_ROLLBACK)
?Silberschatz,Korth and Sudarshan4.69Database System Concepts
ODBC Conformance Levels
? Conformance levels specify subsets of the functionality defined
by the standard.
? Core
? Level 1 requires support for metadata querying
? Level 2 requires ability to send and retrieve arrays of parameter
values and more detailed catalog information.
? SQL Call Level Interface (CLI) standard similar to ODBC
interface,but with some minor differences.
?Silberschatz,Korth and Sudarshan4.70Database System Concepts
JDBC
? JDBC is a Java API for communicating with database systems
supporting SQL
? JDBC supports a variety of features for querying and updating
data,and for retrieving query results
? JDBC also supports metadata retrieval,such as querying about
relations present in the database and the names and types of
relation attributes
? Model for communicating with the database:
? Open a connection
? Create a,statement” object
? Execute queries using the Statement object to send queries and
fetch results
? Exception mechanism to handle errors
?Silberschatz,Korth and Sudarshan4.71Database System Concepts
JDBC Code
public static void JDBCexample(String dbid,String userid,String passwd)
{
try {
Class.forName ("oracle.jdbc.driver.OracleDriver");
Connection conn = DriverManager.getConnection(
"jdbc:oracle:thin:@aura.bell-labs.com:2000:bankdb",userid,passwd);
Statement stmt = conn.createStatement();
… Do Actual Work ….
stmt.close();
conn.close();
}
catch (SQLException sqle) {
System.out.println("SQLException, " + sqle);
}
}
?Silberschatz,Korth and Sudarshan4.72Database System Concepts
JDBC Code (Cont.)
? Update to database
try {
stmt.executeUpdate( "insert into account values
('A-9732','Perryridge',1200)");
} catch (SQLException sqle) {
System.out.println("Could not insert tuple," + sqle);
}
? Execute query and fetch and print results
ResultSet rset = stmt.executeQuery( "select branch_name,avg(balance)
from account
group by branch_name");
while (rset.next()) {
System.out.println(
rset.getString("branch_name") + " " + rset.getFloat(2));
}
?Silberschatz,Korth and Sudarshan4.73Database System Concepts
JDBC Code Details
? Getting result fields:
? rs.getString(“branchname”) and rs.getString(1) equivalent if
branchname is the first argument of select result.
? Dealing with Null values
int a = rs.getInt(“a”);
if (rs.wasNull()) Systems.out.println(“Got null value”);
?Silberschatz,Korth and Sudarshan4.74Database System Concepts
Prepared Statement
? Prepared statement allows queries to be compiled and executed
multiple times with different arguments
PreparedStatement pStmt = conn.prepareStatement(
“insert into account values(?,?,?)”);
pStmt.setString(1,"A-9732");
pStmt.setString(2,"Perryridge");
pStmt.setInt(3,1200);
pStmt.executeUpdate();
pStmt.setString(1,"A-9733");
pStmt.executeUpdate();
? Beware,If value to be stored in database contains a single quote or
other special character,prepared statements work fine,but creating
a query string and executing it directly would result in a syntax
error!
?Silberschatz,Korth and Sudarshan4.75Database System Concepts
Other SQL Features
? SQL sessions
? client connects to an SQL server,establishing a session
? executes a series of statements
? disconnects the session
? can commit or rollback the work carried out in the session
? An SQL environment contains several components,
including a user identifier,and a schema,which
identifies which of several schemas a session is using.
?Silberschatz,Korth and Sudarshan4.76Database System Concepts
Schemas,Catalogs,and Environments
? Three-level hierarchy for naming relations,
? Database contains multiple catalogs
? each catalog can contain multiple schemas
? SQL objects such as relations and views are contained within a
schema
? e.g,catalog5.bank-schema.account
? Each user has a default catalog and schema,and the
combination is unique to the user.
? Default catalog and schema are set up for a connection
? Catalog and schema can be omitted,defaults are assumed
? Multiple versions of an application (e.g,production and test) can
run under separate schemas
?Silberschatz,Korth and Sudarshan4.77Database System Concepts
Procedural Extensions and Stored
Procedures
? SQL provides a module language
? permits definition of procedures in SQL,with if-then-else statements,
for and while loops,etc.
? more in Chapter 9
? Stored Procedures
? Can store procedures in the database
? then execute them using the call statement
? permit external applications to operate on the database without
knowing about internal details
? These features are covered in Chapter 9 (Object Relational
Databases)
Extra Material on JDBC and
Application Architectures
?Silberschatz,Korth and Sudarshan4.79Database System Concepts
Transactions in JDBC
? As with ODBC,each statement gets committed automatically in
JDBC
? To turn off auto commit use
conn.setAutoCommit(false);
? To commit or abort transactions use
conn.commit() or conn.rollback()
? To turn auto commit on again,use
conn.setAutoCommit(true);
?Silberschatz,Korth and Sudarshan4.80Database System Concepts
Procedure and Function Calls in JDBC
? JDBC provides a class CallableStatement which allows SQL stored
procedures/functions to be invoked.
CallableStatement cs1 = conn.prepareCall(,{call proc (?,?)}” ) ;
CallableStatement cs2 = conn.prepareCall(,{? = call func (?,?)}” );
?Silberschatz,Korth and Sudarshan4.81Database System Concepts
Result Set MetaData
? The class ResultSetMetaData provides information about all the
columns of the ResultSet.
? Instance of this class is obtained by getMetaData( ) function of
ResultSet.
? Provides Functions for getting number of columns,column name,
type,precision,scale,table from which the column is derived etc.
ResultSetMetaData rsmd = rs.getMetaData ( );
for ( int i = 1; i <= rsmd.getColumnCount( ); i++ ) {
String name = rsmd.getColumnName(i);
String typeName = rsmd.getColumnTypeName(i);
}
?Silberschatz,Korth and Sudarshan4.82Database System Concepts
Database Meta Data
? The class DatabaseMetaData provides information about database relations
? Has functions for getting all tables,all columns of the table,primary keys etc.
? E.g,to print column names and types of a relation
DatabaseMetaData dbmd = conn.getMetaData( );
ResultSet rs = dbmd.getColumns( null,“BANK-DB”,“account”,“%” );
//Arguments,catalog,schema-pattern,table-pattern,column-pattern
// Returns,1 row for each column,with several attributes such as
// COLUMN_NAME,TYPE_NAME,etc.
while ( rs.next( ) ) {
System.out.println( rs.getString(“COLUMN_NAME”),
rs.getString(“TYPE_NAME”);
}
? There are also functions for getting information such as
? Foreign key references in the schema
? Database limits like maximum row size,maximum no,of connections,etc
?Silberschatz,Korth and Sudarshan4.83Database System Concepts
Application Architectures
? Applications can be built using one of two architectures
? Two tier model
? Application program running at user site directly uses
JDBC/ODBC to communicate with the database
? Three tier model
? Users/programs running at user sites communicate with an
application server,The application server in turn communicates
with the database
?Silberschatz,Korth and Sudarshan4.84Database System Concepts
Two-tier Model
? E.g,Java code runs at client site and uses JDBC to
communicate with the backend server
? Benefits:
? flexible,need not be restricted to predefined queries
? Problems:
? Security,passwords available at client site,all database operation
possible
? More code shipped to client
? Not appropriate across organizations,or in large ones like
universities
?Silberschatz,Korth and Sudarshan4.85Database System Concepts
Three Tier Model
CGI Program
Database
ServerApplication/HTTPServer Servlets
JDBC
Network
Client Client Client
HTTP/Application Specific Protocol
?Silberschatz,Korth and Sudarshan4.86Database System Concepts
Three-tier Model (Cont.)
? E.g,Web client + Java Servlet using JDBC to talk with database
server
? Client sends request over http or application-specific protocol
? Application or Web server receives request
? Request handled by CGI program or servlets
? Security handled by application at server
? Better security
? Fine granularity security
? Simple client,but only packaged transactions
End of Chapter
?Silberschatz,Korth and Sudarshan4.88Database System Concepts
The loan and borrower Relations
?Silberschatz,Korth and Sudarshan4.89Database System Concepts
The Result of loan inner join borrower
on loan.loan-number = borrower.loan-
number
?Silberschatz,Korth and Sudarshan4.90Database System Concepts
The Result of loan left outer join
borrower on loan-number
?Silberschatz,Korth and Sudarshan4.91Database System Concepts
The Result of loan natural inner join
borrower
?Silberschatz,Korth and Sudarshan4.92Database System Concepts
Join Types and Join Conditions
?Silberschatz,Korth and Sudarshan4.93Database System Concepts
The Result of loan natural right outer
join borrower
?Silberschatz,Korth and Sudarshan4.94Database System Concepts
The Result of loan full outer join
borrower using(loan-number)
?Silberschatz,Korth and Sudarshan4.95Database System Concepts
SQL Data Definition for Part of the Bank Database
Chapter 4,SQL
? Background
? Basic Structure
? Set Operations
? Aggregate Functions
? Null Values
? Nested Subqueries
? Derived Relations
? Views
? Modification of the Database
? Joined Relations
? Data Definition Language
? Embedded SQL,ODBC and JDBC
?Silberschatz,Korth and Sudarshan4.2Database System Concepts
Background
? In 1986,ANSI and ISO published an SQL standard,
called SQL-86
? In 1989,ANSI published an extended standard for SQL,
called SQL-89
? SQL-92 and SQL-1999(SQL3)
? The SQL language has several parts:
? Data-definition language (DDL)
? Interactive data-manipulation language (DML)
? View definition
? Transaction control
? Embedded SQL and dynamic SQL
? Integrity
? Authorization
?Silberschatz,Korth and Sudarshan4.3Database System Concepts
Basic Structure
? A typical SQL query has the form:
select A1,A2,...,An
from r1,r2,...,rm
where P
? Ais represent attributes
? ris represent relations
? P is a predicate.
? This query is equivalent to the relational algebra
expression.
?A1,A2,...,An(?P (r1 x r2 x,.,x rm))
? The result of an SQL query is a relation.
?Silberschatz,Korth and Sudarshan4.4Database System Concepts
The select Clause
? The select clause list the attributes desired in the result
of a query
? corresponds to the projection operation of the
relational algebra
? E.g,find the names of all branches in the loan relation
select branch-name
from loan
? In the,pure” relational algebra syntax,the query would
be,
?branch-name(loan)
?Silberschatz,Korth and Sudarshan4.5Database System Concepts
The select Clause (Cont.)
? SQL allows duplicates in relations as well as in
query results.
? To force the elimination of duplicates,insert the
keyword distinct after select.
? Find the names of all branches in the loan
relations,and remove duplicates
select distinct branch-name
from loan
? The keyword all specifies that duplicates not be
removed.
select all branch-name
from loan
?Silberschatz,Korth and Sudarshan4.6Database System Concepts
The select Clause (Cont.)
? An asterisk in the select clause denotes,all attributes”
select *
from loan
? The select clause can contain arithmetic expressions
involving the operation,+,–,?,and /,and operating
on constants or attributes of tuples.
? The query,
select loan-number,branch-name,amount ? 100
from loan
would return a relation which is the same as the loan
relations,except that the attribute amount is multiplied
by 100.
?Silberschatz,Korth and Sudarshan4.7Database System Concepts
The where Clause
? The where clause specifies conditions that the result
must satisfy
? corresponds to the selection predicate of the
relational algebra,
? To find all loan number for loans made at the
Perryridge branch with loan amounts greater than
$1200.
select loan-number
from loan
where branch-name = ?Perryridge? and
amount > 1200
? Comparison results can be combined using the logical
connectives and,or,and not.
?Silberschatz,Korth and Sudarshan4.8Database System Concepts
The where Clause (Cont.)
? SQL includes a between comparison operator
? E.g,Find the loan number of those loans with loan
amounts between $90,000 and $100,000 (that is,
?$90,000 and ?$100,000)
select loan-number
from loan
where amount between 90000 and 100000
?Silberschatz,Korth and Sudarshan4.9Database System Concepts
The from Clause
? The from clause lists the relations involved in the query
? corresponds to the Cartesian product operation of the
relational algebra.
? Find the Cartesian product borrower x loan
select ?
from borrower,loan
? Find the name,loan number and loan amount of all
customers having a loan at the Perryridge branch.
select customer-name,borrower.loan-number,amount
from borrower,loan
where borrower.loan-number = loan.loan-number and
branch-name = ?Perryridge?
?Silberschatz,Korth and Sudarshan4.10Database System Concepts
The Rename Operation
? The SQL allows renaming relations and attributes using
the as clause:
old-name as new-name
? Find the name,loan number and loan amount of all
customers; rename the column name loan-number as
loan-id.
select customer-name,borrower.loan-number as
loan-id,amount
from borrower,loan
where borrower.loan-number = loan.loan-number
?Silberschatz,Korth and Sudarshan4.11Database System Concepts
Tuple Variables
? Tuple variables are defined in the from clause via the
use of the as clause.
? Find the customer names and their loan numbers for
all customers having a loan at some branch.
select distinct T.branch-name
from branch as T,branch as S
where T.assets > S.assets and S.branch-city = ?Brooklyn?
? Find the names of all branches that have greater
assets than some branch located in Brooklyn.
select customer-name,T.loan-number,S.amount
from borrower as T,loan as S
where T.loan-number = S.loan-number
?Silberschatz,Korth and Sudarshan4.12Database System Concepts
String Operations
? SQL includes a string-matching operator for comparisons on
character strings,Patterns are described using two special
characters:
? percent (%),The % character matches any substring.
? underscore (_),The _ character matches any character.
? Find the names of all customers whose street includes the
substring,Main”.
select customer-name
from customer
where customer-street like ‘%Main%’
? SQL supports a variety of string operations such as
? concatenation (using,||”)
? converting from upper to lower case (and vice versa)
? finding string length,extracting substrings,etc.
?Silberschatz,Korth and Sudarshan4.13Database System Concepts
Ordering the Display of Tuples
? List in alphabetic order the names of all customers having a
loan in Perryridge branch
select distinct customer-name
from borrower,loan
where borrower loan-number = loan.loan-number and
branch-name = ‘Perryridge’
order by customer-name
? We may specify desc for descending order or asc for
ascending order,for each attribute; ascending order is the
default.
? E.g,order by customer-name desc
?Silberschatz,Korth and Sudarshan4.14Database System Concepts
Set Operations
? The set operations union,intersect,and except operate on
relations and correspond to the relational algebra operations
????????
? Each of the above operations automatically eliminates
duplicates; to retain all duplicates use the corresponding
multiset versions union all,intersect all and except all.
Suppose a tuple occurs m times in r and n times in s,then,it
occurs:
? m + n times in r union all s
? min(m,n) times in r intersect all s
? max(0,m – n) times in r except all s
?Silberschatz,Korth and Sudarshan4.15Database System Concepts
Set Operations
? Find all customers who have a loan,an account,or both:
(select customer-name from depositor)
except
(select customer-name from borrower)
(select customer-name from depositor)
intersect
(select customer-name from borrower)
? Find all customers who have an account but no loan.
(select customer-name from depositor)
union
(select customer-name from borrower)
? Find all customers who have both a loan and an account.
?Silberschatz,Korth and Sudarshan4.16Database System Concepts
Aggregate Functions
? These functions operate on the multiset of values of a
column of a relation,and return a value
avg,average value
min,minimum value
max,maximum value
sum,sum of values
count,number of values
?Silberschatz,Korth and Sudarshan4.17Database System Concepts
Aggregate Functions (Cont.)
? Find the average account balance at the Perryridge branch.
? Find the number of depositors in the bank.
? Find the number of tuples in the customer relation.
select avg (balance)
from account
where branch-name = ?Perryridge?
select count (*)
from customer
select count (distinct customer-name)
from depositor
?Silberschatz,Korth and Sudarshan4.18Database System Concepts
Aggregate Functions – Group By
? Find the number of depositors for each branch.
Note,Attributes in select clause outside of aggregate
functions must appear in group by list
select branch-name,count (distinct customer-name)
from depositor,account
where depositor.account-number
= account.account-number
group by branch-name
?Silberschatz,Korth and Sudarshan4.19Database System Concepts
Aggregate Functions – Having Clause
? Find the names of all branches where the average
account balance is more than $1,200.
Note,predicates in the having clause are applied after
the formation of groups whereas predicates in the
where clause are applied before forming groups
select branch-name,avg (balance)
from account
group by branch-name
having avg (balance) > 1200
?Silberschatz,Korth and Sudarshan4.20Database System Concepts
Null Values
? It is possible for tuples to have a null value,denoted by null,
for some of their attributes
? null signifies an unknown value or that a value does not
exist.
? The predicate is null can be used to check for null values.
? E.g,Find all loan number which appear in the loan
relation with null values for amount.
select loan-number
from loan
where amount is null
? The result of any arithmetic expression involving null is null
? E.g,5 + null returns null
?Silberschatz,Korth and Sudarshan4.21Database System Concepts
Null Values and Three Valued Logic
? Any comparison with null returns unknown
? E.g,5 < null or null <> null or null = null
? Three-valued logic using the truth value unknown:
? OR,(unknown or true) = true,(unknown or false) =
unknown,(unknown or unknown) = unknown
? AND,(true and unknown) = unknown,(false and
unknown) = false,(unknown and unknown) = unknown
? NOT,(not unknown) = unknown
?,P is unknown” evaluates to true if predicate P
evaluates to unknown
?Silberschatz,Korth and Sudarshan4.22Database System Concepts
Null Values and Aggregates
? Total all loan amounts
select sum (amount)
from loan
? Above statement ignores null amounts
? result is null if there is no non-null amount
? All aggregate operations except count(*) ignore
tuples with null values on the aggregated attributes.
?Silberschatz,Korth and Sudarshan4.23Database System Concepts
Nested Subqueries
? SQL provides a mechanism for the nesting of
subqueries.
? A subquery is a select-from-where expression that is
nested within another query.
? A common use of subqueries is to perform tests for
set membership,set comparisons,and set cardinality.
?Silberschatz,Korth and Sudarshan4.24Database System Concepts
Example Query
? Find all customers who have both an account and a
loan at the bank.
? Find all customers who have a loan at the bank but
do not have an account at the bank
select distinct customer-name
from borrower
where customer-name not in (select customer-name
from depositor)
select distinct customer-name
from borrower
where customer-name in (select customer-name
from depositor)
?Silberschatz,Korth and Sudarshan4.25Database System Concepts
Example Query
? Find all customers who have both an account and a
loan at the Perryridge branch
select distinct customer-name
from borrower,loan
where borrower.loan-number = loan.loan-number and
branch-name =,Perryridge” and
(branch-name,customer-name) in
(select branch-name,customer-name
from depositor,account
where depositor.account-number =
account.account-number)
?Silberschatz,Korth and Sudarshan4.26Database System Concepts
Set Comparison
? Find all branches that have greater assets than some
branch located in Brooklyn.
? Same query using > some clause (至少比一个要大 )
select branch-name
from branch
where assets > some
(select assets
from branch
where branch-city = ‘Brooklyn’)
select distinct T.branch-name
from branch as T,branch as S
where T.assets > S.assets and
S.branch-city = ‘Brooklyn’
?Silberschatz,Korth and Sudarshan4.27Database System Concepts
Example Query
? Find the names of all branches that have greater
assets than all branches located in Brooklyn.
select branch-name
from branch
where assets > all
(select assets
from branch
where branch-city = ?Brooklyn?)
(大于所有的 )
?Silberschatz,Korth and Sudarshan4.28Database System Concepts
Example Query
? Find all customers who have an account at all branches
located in Brooklyn.
select distinct S.customer-name
from depositor as S
where not exists (
(select branch-name
from branch
where branch-city = ?Brooklyn?)
except
(select R.branch-name
from depositor as T,account as R
where T.account-number = R.account-number and
S.customer-name = T.customer-name))
?Silberschatz,Korth and Sudarshan4.29Database System Concepts
Test for Absence of Duplicate Tuples
? The unique construct tests whether a subquery has any
duplicate tuples in its result.
? Find all customers who have at most one account at the
Perryridge branch.
select T.customer-name
from depositor as T
where unique (
select R.customer-name
from account,depositor as R
where T.customer-name = R.customer-name and
R.account-number = account.account-number and
account.branch-name = ?Perryridge?)
? (Schema used in this example)
?Silberschatz,Korth and Sudarshan4.30Database System Concepts
Example Query
? Find all customers who have at least two accounts at the
Perryridge branch,
select distinct T.customer-name
from depositor T
where not unique (
select R.customer-name
from account,depositor as R
where T.customer-name = R.customer-name
and
R.account-number = account.account-number
and
account.branch-name = ‘Perryridge’)
?(Schema used in this example)
?Silberschatz,Korth and Sudarshan4.31Database System Concepts
Views
? Provide a mechanism to hide certain data from the view of
certain users,To create a view we use the command:
create view v as <query expression>
where:
?<query expression> is any legal expression
?The view name is represented by v
?Silberschatz,Korth and Sudarshan4.32Database System Concepts
Example Queries
? A view consisting of branches and their customers
? Find all customers of the Perryridge branch
create view all-customer as
(select branch-name,customer-name
from depositor,account
where depositor.account-number = account.account-number)
union
(select branch-name,customer-name
from borrower,loan
where borrower.loan-number = loan.loan-number)
select customer-name
from all-customer
where branch-name = ?Perryridge?
?Silberschatz,Korth and Sudarshan4.33Database System Concepts
Derived Relations
? Find the average account balance of those branches where the
average account balance is greater than $1200.
select branch-name,avg-balance
from (select branch-name,avg (balance)
from account
group by branch-name)
as result (branch-name,avg-balance)
where avg-balance > 1200
Note that we do not need to use the having clause,since we
compute the temporary (view) relation result in the from clause,
and the attributes of result can be used directly in the where
clause.
?Silberschatz,Korth and Sudarshan4.34Database System Concepts
With Clause
? With clause allows views to be defined locally to a query,rather
than globally,Analogous to procedures in a programming
language.
? Find all accounts with the maximum balance
with max-balance(value) as
select max (balance)
from account
select account-number
from account,max-balance
where account.balance = max-balance.value
?Silberschatz,Korth and Sudarshan4.35Database System Concepts
Complex Query using With Clause
? Find all branches where the total account deposit is greater than
the average of the total account deposits at all branches.
with branch-total (branch-name,value) as
select branch-name,sum (balance)
from account
group by branch-name
with branch-total-avg(value) as
select avg (value)
from branch-total
select branch-name
from branch-total,branch-total-avg
where branch-total.value >= branch-total-avg.value
?Silberschatz,Korth and Sudarshan4.36Database System Concepts
Modification of the Database – Deletion
? Delete all account records at the Perryridge branch
delete from account
where branch-name = ‘Perryridge’
? Delete all accounts at every branch located in Needham city.
delete from account
where branch-name in (select branch-name
from branch
where branch-city = ‘Needham’)
delete from depositor
where account-number in
(select account-number
from branch,account
where branch-city = ‘Needham’
and branch.branch-name = account.branch-name)
? (Schema used in this example)
?Silberschatz,Korth and Sudarshan4.37Database System Concepts
Example Query
? Delete the record of all accounts with balances below the
average at the bank.
delete from account
where balance < (select avg (balance)
from account)
? Problem,as we delete tuples from deposit,the average balance
changes
? Solution used in SQL:
1,First,compute avg balance and find all tuples to delete
2,Next,delete all tuples found above (without recomputing avg or
retesting the tuples)
?Silberschatz,Korth and Sudarshan4.38Database System Concepts
Modification of the Database – Insertion
? Add a new tuple to account
insert into account
values (?A-9732?,?Perryridge?,1200)
or equivalently
insert into account (branch-name,balance,account-number)
values (?Perryridge?,1200,?A-9732?)
? Add a new tuple to account with balance set to null
insert into account
values (?A-777?,?Perryridge?,null)
?Silberschatz,Korth and Sudarshan4.39Database System Concepts
Modification of the Database – Insertion
? Provide as a gift for all loan customers of the Perryridge branch,a
$200 savings account,Let the loan number serve as the account
number for the new savings account
insert into account
select loan-number,branch-name,200
from loan
where branch-name = ?Perryridge?
insert into depositor
select customer-name,loan-number
from loan,borrower
where branch-name = ?Perryridge?
and loan.account-number = borrower.account-number
? The select from where statement is fully evaluated before any of its
results are inserted into the relation (otherwise queries like
insert into table1 select * from table1
would cause problems
?Silberschatz,Korth and Sudarshan4.40Database System Concepts
Modification of the Database – Updates
? Increase all accounts with balances over $10,000 by 6%,all
other accounts receive 5%.
? Write two update statements:
update account
set balance = balance ? 1.06
where balance > 10000
update account
set balance = balance ? 1.05
where balance ? 10000
? The order is important
? Can be done better using the case statement (next slide)
?Silberschatz,Korth and Sudarshan4.41Database System Concepts
Case Statement for Conditional Updates
? Same query as before,Increase all accounts with balances over
$10,000 by 6%,all other accounts receive 5%.
update account
set balance = case
when balance <= 10000 then balance *1.05
else balance * 1.06
end
?Silberschatz,Korth and Sudarshan4.42Database System Concepts
Update of a View
? Create a view of all loan data in loan relation,hiding the amount
attribute
create view branch-loan as
select branch-name,loan-number
from loan
? Add a new tuple to branch-loan
insert into branch-loan
values (?Perryridge?,?L-307?)
This insertion must be represented by the insertion of the tuple
(?L-307?,?Perryridge?,null)
into the loan relation
? Updates on more complex views are difficult or impossible to
translate,and hence are disallowed,
? Most SQL implementations allow updates only on simple views
(without aggregates) defined on a single relation
?Silberschatz,Korth and Sudarshan4.43Database System Concepts
Transactions
? A transaction is a sequence of queries and update statements executed
as a single unit
? Transactions are started implicitly and terminated by one of
? commit work,makes all updates of the transaction permanent in the
database
? rollback work,undoes all updates performed by the transaction,
? Motivating example
? Transfer of money from one account to another involves two steps:
? deduct from one account and credit to another
? If one steps succeeds and the other fails,database is in an inconsistent state
? Therefore,either both steps should succeed or neither should
? If any step of a transaction fails,all work done by the transaction can be
undone by rollback work,
? Rollback of incomplete transactions is done automatically,in case of
system failures
?Silberschatz,Korth and Sudarshan4.44Database System Concepts
Transactions (Cont.)
? In most database systems,each SQL statement that executes
successfully is automatically committed,
? Each transaction would then consist of only a single statement
? Automatic commit can usually be turned off,allowing multi-
statement transactions,but how to do so depends on the database
system
? Another option in SQL:1999,enclose statements within
begin atomic
…
end
?Silberschatz,Korth and Sudarshan4.45Database System Concepts
Joined Relations
? Join operations take two relations and return as a result another
relation.
? These additional operations are typically used as subquery
expressions in the from clause
? Join condition – defines which tuples in the two relations match,
and what attributes are present in the result of the join.
? Join type – defines how tuples in each relation that do not match
any tuple in the other relation (based on the join condition) are
treated.
Join Types
inner join
left outer join
right outer join
full outer join
Join Conditions
natural
on <predicate>
using (A1,A2,...,An)
?Silberschatz,Korth and Sudarshan4.46Database System Concepts
Joined Relations – Datasets for Examples
? Relation loan
? Relation borrower
customer-name loan-number
Jones
Smith
Hayes
L-170
L-230
L-155
amount
3000
4000
1700
branch-name
Downtown
Redwood
Perryridge
loan-number
L-170
L-230
L-260
? Note,borrower information missing for L-260 and loan
information missing for L-155
?Silberschatz,Korth and Sudarshan4.47Database System Concepts
Joined Relations – Examples
? loan inner join borrower on
loan.loan-number = borrower.loan-number
? loan left outer join borrower on
loan.loan-number = borrower.loan-number
branch-name amount
Downtown
Redwood
3000
4000
customer-name loan-number
Jones
Smith
L-170
L-230
loan-number
L-170
L-230
branch-name amount
Downtown
Redwood
Perryridge
3000
4000
1700
customer-name loan-number
Jones
Smith
null
L-170
L-230
null
loan-number
L-170
L-230
L-260
?Silberschatz,Korth and Sudarshan4.48Database System Concepts
Joined Relations – Examples
? loan natural inner join borrower
? loan natural right outer join borrower
branch-name amount
Downtown
Redwood
3000
4000
customer-name
Jones
Smith
loan-number
L-170
L-230
branch-name amount
Downtown
Redwood
null
3000
4000
null
customer-name
Jones
Smith
Hayes
loan-number
L-170
L-230
L-155
?Silberschatz,Korth and Sudarshan4.49Database System Concepts
Joined Relations – Examples
? loan full outer join borrower using (loan-number)
? Find all customers who have either an account or a loan (but
not both) at the bank.
branch-name amount
Downtown
Redwood
Perryridge
null
3000
4000
1700
null
customer-name
Jones
Smith
null
Hayes
loan-number
L-170
L-230
L-260
L-155
select customer-name
from (depositor natural full outer join borrower)
where account-number is null or loan-number is null
?Silberschatz,Korth and Sudarshan4.50Database System Concepts
Data Definition Language (DDL)
? The schema for each relation.
? The domain of values associated with each attribute.
? Integrity constraints
? The set of indices to be maintained for each relations.
? Security and authorization information for each relation.
? The physical storage structure of each relation on disk.
Allows the specification of not only a set of relations but also
information about each relation,including:
?Silberschatz,Korth and Sudarshan4.51Database System Concepts
Domain Types in SQL
? char(n),Fixed length character string,with user-specified length n.
? varchar(n),Variable length character strings,with user-specified maximum
length n.
? int,Integer (a finite subset of the integers that is machine-dependent).
? smallint,Small integer (a machine-dependent subset of the integer
domain type).
? numeric(p,d),Fixed point number,with user-specified precision of p digits,
with n digits to the right of decimal point,
? real,double precision,Floating point and double-precision floating point
numbers,with machine-dependent precision.
? float(n),Floating point number,with user-specified precision of at least n
digits.
? Null values are allowed in all the domain types,Declaring an attribute to be
not null prohibits null values for that attribute.
? create domain construct in SQL-92 creates user-defined domain types
create domain person-name char(20) not null
?Silberschatz,Korth and Sudarshan4.52Database System Concepts
Date/Time Types in SQL (Cont.)
? date,Dates,containing a (4 digit) year,month and date
? E.g,date ?2001-7-27?
? time,Time of day,in hours,minutes and seconds.
? E.g,time ?09:00:30? time ?09:00:30.75?
? timestamp,date plus time of day
? E.g,timestamp ?2001-7-27 09:00:30.75?
? Interval,period of time
? E.g,Interval ?1? day
? Subtracting a date/time/timestamp value from another gives an interval value
? Interval values can be added to date/time/timestamp values
? Can extract values of individual fields from date/time/timestamp
? E.g,extract (year from r.starttime)
? Can cast string types to date/time/timestamp
? E.g,cast <string-valued-expression> as date
?Silberschatz,Korth and Sudarshan4.53Database System Concepts
Create Table Construct
? An SQL relation is defined using the create table
command:
create table r (A1 D1,A2 D2,...,An Dn,
(integrity-constraint1),
...,
(integrity-constraintk))
? r is the name of the relation
? each Ai is an attribute name in the schema of relation r
? Di is the data type of values in the domain of attribute Ai
? Example:
create table branch
(branch-name char(15) not null,
branch-city char(30),
assets integer)
?Silberschatz,Korth and Sudarshan4.54Database System Concepts
Integrity Constraints in Create Table
? not null
? primary key (A1,...,An)
? check (P),where P is a predicate
Example,Declare branch-name as the primary key for
branch and ensure that the values of assets are non-
negative.
create table branch
(branch-namechar(15),
branch-city char(30)
assets integer,
primary key (branch-name),
check (assets >= 0))
primary key declaration on an attribute automatically
ensures not null in SQL-92 onwards,needs to be
explicitly stated in SQL-89
?Silberschatz,Korth and Sudarshan4.55Database System Concepts
Drop and Alter Table Constructs
? The drop table command deletes all information about the
dropped relation from the database.
? The alter table command is used to add attributes to an
existing relation,
alter table r add A D
where A is the name of the attribute to be added to relation r
and D is the domain of A.
? All tuples in the relation are assigned null as the value for the
new attribute,
? The alter table command can also be used to drop attributes
of a relation
alter table r drop A
where A is the name of an attribute of relation r
? Dropping of attributes not supported by many databases
?Silberschatz,Korth and Sudarshan4.56Database System Concepts
Embedded SQL
? The SQL standard defines embeddings of SQL in a variety of
programming languages such as Pascal,PL/I,Fortran,C,and
Cobol.
? A language to which SQL queries are embedded is referred to as
a host language,and the SQL structures permitted in the host
language comprise embedded SQL.
? The basic form of these languages follows that of the System R
embedding of SQL into PL/I.
? EXEC SQL statement is used to identify embedded SQL request
to the preprocessor
EXEC SQL <embedded SQL statement > END-EXEC
Note,this varies by language,E.g,the Java embedding uses
# SQL { …,} ;
?Silberschatz,Korth and Sudarshan4.57Database System Concepts
Example Query
? Specify the query in SQL and declare a cursor for it
EXEC SQL
declare c cursor for
select customer-name,customer-city
from depositor,customer,account
where depositor.customer-name = customer.customer-name
and depositor account-number = account.account-number
and account.balance >,amount
END-EXEC
From within a host language,find the names and cities of
customers with more than the variable amount dollars in some
account.
?Silberschatz,Korth and Sudarshan4.58Database System Concepts
Example Query
Query1->Close();
Query1->SQL->Clear();
Query1->SQL->Add("SELECT*from船名 WHERE编码 =:DM");
Query1->ParamByName("DM")->AsString=DBEdit1->Text;
Query1->Open();
while(!Query1->Eof)
{
DM=Query1->FieldByName("编码 ")->AsString+" ";
ZD=Query1->FieldByName("船名 ")->AsString;
LENGTH[i]=DM.Length();
Z_LENGTH[i]=(DM+ZD).Length();
ListBox1->Items->Add(DM+ZD);
i=i+1;
Query1->Next();
}
?Silberschatz,Korth and Sudarshan4.59Database System Concepts
Embedded SQL (Cont.)
? The open statement causes the query to be evaluated
EXEC SQL open c END-EXEC
? The fetch statement causes the values of one tuple in the query
result to be placed on host language variables.
EXEC SQL fetch c into,cn,:cc END-EXEC
Repeated calls to fetch get successive tuples in the query result
? A variable called SQLSTATE in the SQL communication area
(SQLCA) gets set to ?02000? to indicate no more data is available
? The close statement causes the database system to delete the
temporary relation that holds the result of the query.
EXEC SQL close c END-EXEC
Note,above details vary with language,E.g,the Java embedding
defines Java iterators to step through result tuples.
?Silberschatz,Korth and Sudarshan4.60Database System Concepts
Updates Through Cursors
? Can update tuples fetched by cursor by declaring that the cursor
is for update
declare c cursor for
select *
from account
where branch-name= ?Perryridge?
for update
? To update tuple at the current location of cursor
update account
set balance = balance + 100
where current of c
?Silberschatz,Korth and Sudarshan4.61Database System Concepts
Dynamic SQL
? Allows programs to construct and submit SQL queries at run
time.
? Example of the use of dynamic SQL from within a C program.
char * sqlprog =,update account
set balance = balance * 1.05
where account-number =?”
EXEC SQL prepare dynprog from,sqlprog;
char account [10] =,A-101”;
EXEC SQL execute dynprog using,account;
? The dynamic SQL program contains a?,which is a place holder
for a value that is provided when the SQL program is executed.
?Silberschatz,Korth and Sudarshan4.62Database System Concepts
Dynamic SQL
sSQL = "select * from 出港集装箱信息表 WHERE " + CXTJ +"
ORDER BY出港时间 ";
Query2->Close();
Query2->SQL->Clear();
Query2->SQL->Add(sSQL);
Query2->Open();
for(inti=0; i<Query2->RecordCount; i++)
{
for(int j = 0; j < ListBox3->Items->Count; j++)
Sh1.PG("Cells",i+3,j+1).PS("Value",Query2->Fields->Fields[j]-
>AsString) ;
Query2->Next();
}
?Silberschatz,Korth and Sudarshan4.63Database System Concepts
ODBC
? Open DataBase Connectivity(ODBC) standard
? standard for application program to communicate with a database
server.
? application program interface (API) to
? open a connection with a database,
? send queries and updates,
? get back results.
? Applications such as GUI,spreadsheets,etc,can use ODBC
?Silberschatz,Korth and Sudarshan4.64Database System Concepts
ODBC (Cont.)
? Each database system supporting ODBC provides a "driver" library that
must be linked with the client program.
? When client program makes an ODBC API call,the code in the library
communicates with the server to carry out the requested action,and
fetch results.
? ODBC program first allocates an SQL environment,then a database
connection handle.
? Opens database connection using SQLConnect(),Parameters for
SQLConnect:
? connection handle,
? the server to which to connect
? the user identifier,
? password
? Must also specify types of arguments:
? SQL_NTS denotes previous argument is a null-terminated string.
?Silberschatz,Korth and Sudarshan4.65Database System Concepts
ODBC Code
? int ODBCexample()
{
RETCODE error;
HENV env; /* environment */
HDBC conn; /* database connection */
SQLAllocEnv(&env);
SQLAllocConnect(env,&conn);
SQLConnect(conn,"aura.bell-labs.com",SQL_NTS,"avi",SQL_NTS,
"avipasswd",SQL_NTS);
{ …,Do actual work … }
SQLDisconnect(conn);
SQLFreeConnect(conn);
SQLFreeEnv(env);
}
?Silberschatz,Korth and Sudarshan4.66Database System Concepts
ODBC Code (Cont.)
? Program sends SQL commands to the database by using SQLExecDirect
? Result tuples are fetched using SQLFetch()
? SQLBindCol() binds C language variables to attributes of the query result
? When a tuple is fetched,its attribute values are automatically stored in
corresponding C variables.
? Arguments to SQLBindCol()
– ODBC stmt variable,attribute position in query result
– The type conversion from SQL to C,
– The address of the variable,
– For variable-length types like character arrays,
? The maximum length of the variable
? Location to store actual length when a tuple is fetched.
? Note,A negative value returned for the length field indicates null
value
? Good programming requires checking results of every function call for
errors; we have omitted most checks for brevity.
?Silberschatz,Korth and Sudarshan4.67Database System Concepts
ODBC Code (Cont.)
? Main body of program
char branchname[80];
float balance;
int lenOut1,lenOut2;
HSTMT stmt;
SQLAllocStmt(conn,&stmt);
char * sqlquery = "select branch_name,sum (balance)
from account
group by branch_name";
error = SQLExecDirect(stmt,sqlquery,SQL_NTS);
if (error == SQL_SUCCESS) {
SQLBindCol(stmt,1,SQL_C_CHAR,branchname,80,&lenOut1);
SQLBindCol(stmt,2,SQL_C_FLOAT,&balance,0,&lenOut2);
while (SQLFetch(stmt) >= SQL_SUCCESS) {
printf (" %s %g\n",branchname,balance);
}
}
SQLFreeStmt(stmt,SQL_DROP);
?Silberschatz,Korth and Sudarshan4.68Database System Concepts
More ODBC Features
? Prepared Statement
? SQL statement prepared,compiled at the database
? Can have placeholders,E.g,insert into account values(?,?,?)
? Repeatedly executed with actual values for the placeholders
? Metadata features
? finding all the relations in the database and
? finding the names and types of columns of a query result or a relation in
the database.
? By default,each SQL statement is treated as a separate transaction
that is committed automatically.
? Can turn off automatic commit on a connection
? SQLSetConnectOption(conn,SQL_AUTOCOMMIT,0)}
? transactions must then be committed or rolled back explicitly by
? SQLTransact(conn,SQL_COMMIT) or
? SQLTransact(conn,SQL_ROLLBACK)
?Silberschatz,Korth and Sudarshan4.69Database System Concepts
ODBC Conformance Levels
? Conformance levels specify subsets of the functionality defined
by the standard.
? Core
? Level 1 requires support for metadata querying
? Level 2 requires ability to send and retrieve arrays of parameter
values and more detailed catalog information.
? SQL Call Level Interface (CLI) standard similar to ODBC
interface,but with some minor differences.
?Silberschatz,Korth and Sudarshan4.70Database System Concepts
JDBC
? JDBC is a Java API for communicating with database systems
supporting SQL
? JDBC supports a variety of features for querying and updating
data,and for retrieving query results
? JDBC also supports metadata retrieval,such as querying about
relations present in the database and the names and types of
relation attributes
? Model for communicating with the database:
? Open a connection
? Create a,statement” object
? Execute queries using the Statement object to send queries and
fetch results
? Exception mechanism to handle errors
?Silberschatz,Korth and Sudarshan4.71Database System Concepts
JDBC Code
public static void JDBCexample(String dbid,String userid,String passwd)
{
try {
Class.forName ("oracle.jdbc.driver.OracleDriver");
Connection conn = DriverManager.getConnection(
"jdbc:oracle:thin:@aura.bell-labs.com:2000:bankdb",userid,passwd);
Statement stmt = conn.createStatement();
… Do Actual Work ….
stmt.close();
conn.close();
}
catch (SQLException sqle) {
System.out.println("SQLException, " + sqle);
}
}
?Silberschatz,Korth and Sudarshan4.72Database System Concepts
JDBC Code (Cont.)
? Update to database
try {
stmt.executeUpdate( "insert into account values
('A-9732','Perryridge',1200)");
} catch (SQLException sqle) {
System.out.println("Could not insert tuple," + sqle);
}
? Execute query and fetch and print results
ResultSet rset = stmt.executeQuery( "select branch_name,avg(balance)
from account
group by branch_name");
while (rset.next()) {
System.out.println(
rset.getString("branch_name") + " " + rset.getFloat(2));
}
?Silberschatz,Korth and Sudarshan4.73Database System Concepts
JDBC Code Details
? Getting result fields:
? rs.getString(“branchname”) and rs.getString(1) equivalent if
branchname is the first argument of select result.
? Dealing with Null values
int a = rs.getInt(“a”);
if (rs.wasNull()) Systems.out.println(“Got null value”);
?Silberschatz,Korth and Sudarshan4.74Database System Concepts
Prepared Statement
? Prepared statement allows queries to be compiled and executed
multiple times with different arguments
PreparedStatement pStmt = conn.prepareStatement(
“insert into account values(?,?,?)”);
pStmt.setString(1,"A-9732");
pStmt.setString(2,"Perryridge");
pStmt.setInt(3,1200);
pStmt.executeUpdate();
pStmt.setString(1,"A-9733");
pStmt.executeUpdate();
? Beware,If value to be stored in database contains a single quote or
other special character,prepared statements work fine,but creating
a query string and executing it directly would result in a syntax
error!
?Silberschatz,Korth and Sudarshan4.75Database System Concepts
Other SQL Features
? SQL sessions
? client connects to an SQL server,establishing a session
? executes a series of statements
? disconnects the session
? can commit or rollback the work carried out in the session
? An SQL environment contains several components,
including a user identifier,and a schema,which
identifies which of several schemas a session is using.
?Silberschatz,Korth and Sudarshan4.76Database System Concepts
Schemas,Catalogs,and Environments
? Three-level hierarchy for naming relations,
? Database contains multiple catalogs
? each catalog can contain multiple schemas
? SQL objects such as relations and views are contained within a
schema
? e.g,catalog5.bank-schema.account
? Each user has a default catalog and schema,and the
combination is unique to the user.
? Default catalog and schema are set up for a connection
? Catalog and schema can be omitted,defaults are assumed
? Multiple versions of an application (e.g,production and test) can
run under separate schemas
?Silberschatz,Korth and Sudarshan4.77Database System Concepts
Procedural Extensions and Stored
Procedures
? SQL provides a module language
? permits definition of procedures in SQL,with if-then-else statements,
for and while loops,etc.
? more in Chapter 9
? Stored Procedures
? Can store procedures in the database
? then execute them using the call statement
? permit external applications to operate on the database without
knowing about internal details
? These features are covered in Chapter 9 (Object Relational
Databases)
Extra Material on JDBC and
Application Architectures
?Silberschatz,Korth and Sudarshan4.79Database System Concepts
Transactions in JDBC
? As with ODBC,each statement gets committed automatically in
JDBC
? To turn off auto commit use
conn.setAutoCommit(false);
? To commit or abort transactions use
conn.commit() or conn.rollback()
? To turn auto commit on again,use
conn.setAutoCommit(true);
?Silberschatz,Korth and Sudarshan4.80Database System Concepts
Procedure and Function Calls in JDBC
? JDBC provides a class CallableStatement which allows SQL stored
procedures/functions to be invoked.
CallableStatement cs1 = conn.prepareCall(,{call proc (?,?)}” ) ;
CallableStatement cs2 = conn.prepareCall(,{? = call func (?,?)}” );
?Silberschatz,Korth and Sudarshan4.81Database System Concepts
Result Set MetaData
? The class ResultSetMetaData provides information about all the
columns of the ResultSet.
? Instance of this class is obtained by getMetaData( ) function of
ResultSet.
? Provides Functions for getting number of columns,column name,
type,precision,scale,table from which the column is derived etc.
ResultSetMetaData rsmd = rs.getMetaData ( );
for ( int i = 1; i <= rsmd.getColumnCount( ); i++ ) {
String name = rsmd.getColumnName(i);
String typeName = rsmd.getColumnTypeName(i);
}
?Silberschatz,Korth and Sudarshan4.82Database System Concepts
Database Meta Data
? The class DatabaseMetaData provides information about database relations
? Has functions for getting all tables,all columns of the table,primary keys etc.
? E.g,to print column names and types of a relation
DatabaseMetaData dbmd = conn.getMetaData( );
ResultSet rs = dbmd.getColumns( null,“BANK-DB”,“account”,“%” );
//Arguments,catalog,schema-pattern,table-pattern,column-pattern
// Returns,1 row for each column,with several attributes such as
// COLUMN_NAME,TYPE_NAME,etc.
while ( rs.next( ) ) {
System.out.println( rs.getString(“COLUMN_NAME”),
rs.getString(“TYPE_NAME”);
}
? There are also functions for getting information such as
? Foreign key references in the schema
? Database limits like maximum row size,maximum no,of connections,etc
?Silberschatz,Korth and Sudarshan4.83Database System Concepts
Application Architectures
? Applications can be built using one of two architectures
? Two tier model
? Application program running at user site directly uses
JDBC/ODBC to communicate with the database
? Three tier model
? Users/programs running at user sites communicate with an
application server,The application server in turn communicates
with the database
?Silberschatz,Korth and Sudarshan4.84Database System Concepts
Two-tier Model
? E.g,Java code runs at client site and uses JDBC to
communicate with the backend server
? Benefits:
? flexible,need not be restricted to predefined queries
? Problems:
? Security,passwords available at client site,all database operation
possible
? More code shipped to client
? Not appropriate across organizations,or in large ones like
universities
?Silberschatz,Korth and Sudarshan4.85Database System Concepts
Three Tier Model
CGI Program
Database
ServerApplication/HTTPServer Servlets
JDBC
Network
Client Client Client
HTTP/Application Specific Protocol
?Silberschatz,Korth and Sudarshan4.86Database System Concepts
Three-tier Model (Cont.)
? E.g,Web client + Java Servlet using JDBC to talk with database
server
? Client sends request over http or application-specific protocol
? Application or Web server receives request
? Request handled by CGI program or servlets
? Security handled by application at server
? Better security
? Fine granularity security
? Simple client,but only packaged transactions
End of Chapter
?Silberschatz,Korth and Sudarshan4.88Database System Concepts
The loan and borrower Relations
?Silberschatz,Korth and Sudarshan4.89Database System Concepts
The Result of loan inner join borrower
on loan.loan-number = borrower.loan-
number
?Silberschatz,Korth and Sudarshan4.90Database System Concepts
The Result of loan left outer join
borrower on loan-number
?Silberschatz,Korth and Sudarshan4.91Database System Concepts
The Result of loan natural inner join
borrower
?Silberschatz,Korth and Sudarshan4.92Database System Concepts
Join Types and Join Conditions
?Silberschatz,Korth and Sudarshan4.93Database System Concepts
The Result of loan natural right outer
join borrower
?Silberschatz,Korth and Sudarshan4.94Database System Concepts
The Result of loan full outer join
borrower using(loan-number)
?Silberschatz,Korth and Sudarshan4.95Database System Concepts
SQL Data Definition for Part of the Bank Database
