Programming in Oracle with PL/SQL

Procedural Language Extension toSQL

n PL/SQL

n PL/SQL Blocks

n Anonymous blocksn Using select statement

n Using conditions

n Loops

n Printing output

n Named blocksn Functions

n Procedures

n Triggers

PL/SQL

n Allows using general programming tools with SQL, for example: loops, conditions, functions, etc.

n This allows a lot more freedom than general SQL, and is lighter-weight than JDBC.

n We write PL/SQL code in a regular file, for example PL.sql, and load it with @PL in the sqlplus console.

PL/SQL Blocks

n PL/SQL code is built of Blocks, with a unique

structure.

n There are two types of blocks in PL/SQL:

1. Anonymous Blocks: have no name (like scripts)

n can be written and executed immediately in SQLPLUS

n can be used in a trigger

2. Named Blocks:

n Procedures

n Functions

Anonymous Block Structure:

DECLARE (optional)/* Here you declare the variables you will use in this block */

BEGIN (mandatory)/* Here you define the executable statements (what the block

DOES!)*/

EXCEPTION (optional)/* Here you define the actions that take place if an exception is

thrown during the run of this block */

END; (mandatory)/

A correct completion of a block will generate the following message:

PL/SQL procedure successfully completed

DECLARE

Syntax

Examples

identifier [CONSTANT] datatype [NOT NULL] [:= | DEFAULT expr];

Declarebirthday DATE;age NUMBER(2) NOT NULL := 27;name VARCHAR2(13) := 'Levi';magic CONSTANT NUMBER := 77;valid BOOLEAN NOT NULL := TRUE;

SELECT Statements

n INTO clause is required.

n Query must return exactly one row.

n Otherwise, a NO_DATA_FOUND or TOO_MANY_ROWS exception is thrown

DECLAREv_sname VARCHAR2(10);v_rating NUMBER(3);

BEGINSELECT sname, ratingINTO v_sname, v_ratingFROM SailorsWHERE sid = '112';

END;/

Conditional logic

If <cond>

then <command>

elsif <cond2>

then <command2>

else

<command3>

end if;

If <cond>then

if <cond2>then

<command1>end if;

else <command2>end if;

Condition: Nested conditions:

IF-THEN-ELSIF Statements

. . .IF rating > 7 THENv_message := 'You are great';

ELSIF rating >= 5 THEN v_message := 'Not bad';

ELSEv_message := 'Pretty bad';

END IF;. . .

Suppose we have the following table:

n Want to keep track of how many times someone logged on to the DB

n When running, if user is already in table, increment logon_num. Otherwise, insert user into table

create table mylog(

who varchar2(30),

logon_num number

);

2Moshe

4John

3Peter

logon_num

who

mylog

Solution

DECLAREcnt NUMBER;

BEGINselect count(*)into cntfrom mylogwhere who = user;

if cnt > 0 thenupdate mylogset logon_num = logon_num + 1

where who = user;else insert into mylog values(user, 1);

end if;commit;

end;/

Loops: FOR Loop

DECLAREi number_table.num%TYPE;

BEGINFOR i IN 1..10 LOOPINSERT INTO number_table VALUES(i);

END LOOP;END;

Notice that i is incremented automatically

Loops: WHILE Loop

DECLARETEN number:=10;i number_table.num%TYPE:=1;BEGINWHILE i <= TEN LOOP

INSERT INTO number_table VALUES(i);i := i + 1;

END LOOP;END;

Printing Output

n You need to use a function in the DBMS_OUTPUT

package in order to print to the output

n If you want to see the output on the screen, you

must type the following (before starting):

set serveroutput on format wrapped size 1000000

n Then print using

n dbms_output. put_line(your_string);

n dbms_output.put(your_string);

Functions and Procedures

n Up until now, our code was in an anonymous block

n It was run immediately

n It is useful to put code in a function or procedure so it can be called several times

n Once we create a procedure or function in a Database, it will remain until deleted (like a table).

CREATE [OR REPLACE] PROCEDURE procedure_name[(parameter1 [mode1] datatype1,parameter2 [mode2] datatype2,. . .)]

IS|ASPL/SQL Block;

Creating Procedures

n Modes:n IN: procedure must be called with a value for the parameter.

Value cannot be changed

n OUT: procedure must be called with a variable for the parameter. Changes to the parameter are seen by the user (i.e., call by reference)

n IN OUT: value can be sent, and changes to the parameter are seen by the user

n Default Mode is: IN

create or replace procedure num_logged(person IN mylog.who%TYPE,num OUT mylog.logon_num%TYPE)ISBEGIN

select logon_num into numfrom mylogwhere who = person;

END;/

Example- what does this do?

2Joe

4John

3Pete

logon_

numwho

Table mylog

declarehowmany mylog.logon_num%TYPE;

beginnum_logged(‘John',howmany);dbms_output.put_line(howmany);

end;/

Calling the Procedure

Errors in a Procedure

n When creating the procedure, if there are errors in its definition, they will not be shown

n To see the errors of a procedure called myProcedure, type

SHOW ERRORS PROCEDURE myProcedure

in the SQLPLUS prompt

n For functions, type

SHOW ERRORS FUNCTION myFunction

Creating a Function

n Almost exactly like creating a procedure, but you supply a return type

CREATE [OR REPLACE] FUNCTIONfunction_name[(parameter1 [mode1] datatype1,parameter2 [mode2] datatype2,. . .)]

RETURN datatypeIS|ASPL/SQL Block;

create or replace function rating_message(rating IN NUMBER)return VARCHAR2ASBEGINIF rating > 7 THENreturn 'You are great';

ELSIF rating >= 5 THEN return 'Not bad';

ELSEreturn 'Pretty bad';

END IF;END;/

A Function

NOTE THAT YOU DON'T SPECIFY THE

SIZE

declarepaulRate:=9;

Begin dbms_output.put_line(ratingMessage(paulRate));end;/

Calling the function

create or replace function squareFunc(num in number)

return number

is

BEGIN

return num*num;

End;

/

BEGINdbms_output.put_line(squareFunc(3.5));END;/

Creating a function:

Using the function:

Triggers

n A trigger is a statement that is executed automatically by the system as a side effect of a modification to the database.

n To design a trigger mechanism, we must:

n Specify the conditions under which the trigger is to be executed.

n Specify the actions to be taken when the trigger executes.

Trigger Example

n Suppose that instead of allowing negative account balances, the bank deals with overdrafts by n setting the account balance to zero

n creating a loan in the amount of the overdraft

n giving this loan a loan number identical to the account number of the overdrawn account

n The condition for executing the trigger is an update to the account relation that results in a negative balance value.

Trigger Example

create trigger overdraft-trigger after update on account referencing new row as nrow for each rowwhen nrow.balance < 0begin atomic

insert into borrower(select customer-name, account-numberfrom depositorwhere nrow.account-number =

depositor.account-number);insert into loan values

(n.row.account-number, nrow.branch-name, – nrow.balance);

update account set balance = 0where account.account-number = nrow.account-number

end