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PL/SQL programming Procedures and Cursors

Lecture 1

Akhtar Ali

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SQL refresher Basic commands

SELECT, INSERT, DELETE, UPDATE Always remember to state the table(s) you

are selecting data from Join tables using keys (Primary / Foreign) Filter data wherever possible Procedures are different from scripts

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SQL scripts Set of commands to run in sequence. Stored as a text file (e.g. using Notepad) on a disk

and not in the data dictionary. It is accessed by file name

Executed using @ or Start.

Script called:

Create_User.sql

Executed by:

SQL> @Create_User.sql

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Procedures in SQL Block of SQL statements stored in the Data dictionary

and called by applications or from SQL* plus prompt. Usually used to implement application/business logic. When called all code within a procedure is executed

(unlike packages). Action takes place on server side not client. Do not return value to calling program. Not available in Oracle 6 or older. Aid security as DBA will grant access to procedures not

tables, therefore users can not access tables unless via a procedure.

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Building a procedure1. Create or replace command

2. Type of object to be created

3. Name of object

4. Any variables accessed or imported

5. Declare local variables

6. Write body of the object (code)

7. End procedure declaration

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1. Create or replace command

2. Object to be created

3. Name of object

4. Any variables accessed or imported

5. Declare local variables

6. Body

7. End procedure declaration

Create or replace procedure inflation_rise (inf_rate in number)

Begin

update employee

set salary = salary + (salary * inf_rate / 100);

commit;

End;

This procedure is called inflation_rise and used a variable accessed as inf_rate which is a number, this is passed in when the procedure is used. It simply updates the salary by the rate of inflation.

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Compiling and executing procedures Like any program the code needs to be compiled. @inflation_rise will compile the procedure and make

it available in the database Execute inflation_rise(2) will cause the procedure to

execute, with 2 as an inflation rate. Remember to compile a procedure once it has been

amended. For ease of use, it is easiest to write procedures in

notepad, store as script files, and then run them, this means that they can be easily edited – also you will have a copy if required

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ExampleCREATE OR REPLACE PROCEDURE validate_customer ( v_cust IN VARCHAR ) AS

v_count NUMBER;

BEGIN

SELECT COUNT(*) INTO V_COUNT

FROM customer

WHERE c_id = v_cust;

IF v_count > 0 THEN

DBMS_OUTPUT.PUT_LINE( 'customer valid');

ELSE

DBMS_OUTPUT.PUT_LINE('customer not recognised');

END IF;

END;

Any variables passed into procedure

Local variables used by procedure

SQL

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Cursors in SQL Enables users to loop around a selection of

data. Stores data selected from a query in a temp

area for use when opened. Use complex actions which would not be

feasible in standard SQL selection queries

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Syntax for Cursors Declared as a variable in the same way as

standard variables Identified as cursor type SQL included E.g. Cursor cur_emp is

Select emp_id, surname name, grade, salary

From employee

Where regrade is true;

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Cursors A cursor is a temp store of data. The data is populated when the cursor is opened. Once opened the data must be moved from the

temp area to a local variable to be used by the program. These variables must be populated in the same order that the data is held in the cursor.

The data is looped round till an exit clause is reached.

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Active setActive set

Current rowCurrent rowCursor

7369 SMITH CLERK

7566 JONES MANAGER

7788 SCOTT ANALYST

7876 ADAMS CLERK

7902 FORD ANALYST

Cursor FunctionsCursor Functions

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Controlling CursorControlling Cursor

• Create a Create a named named SQL areaSQL area

DECLAREDECLAREDECLAREDECLARE

• Identify Identify the active the active setset

OPENOPENOPENOPEN

• Load the Load the current current row into row into variablesvariables

FETCHFETCHFETCHFETCH

• Test for Test for existing existing rowsrows

EMPTY?

• Return to Return to FETCH if FETCH if rows rows foundfound

NoNo

• Release Release the active the active setset

CLOSECLOSECLOSECLOSEYesYes

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Controlling Cursor…Controlling Cursor…Open the cursor.Open the cursor.

CursorCursor

PointerPointer

Fetch a row from the cursor.Fetch a row from the cursor.

CursorCursor

PointerPointer

Continue until empty.Continue until empty.

CursorCursor

PointerPointer

Close the cursor.Close the cursor.

CursorCursor

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Cursor AttributesCursor Attributes

Attribute Type Description

%ISOPEN Boolean Evaluates to TRUE if the cursor is open

%NOTFOUND Boolean Evaluates to TRUE if the most recent fetch does not return a row

%FOUND Boolean Evaluates to TRUE if the mostrecent fetch returns a row; complement of %NOTFOUND

%ROWCOUNT Number Evaluates to the total number of rows returned so far

Obtain status information about a cursor.

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Create or replace procedure proc_test as

v_empid number;

Cursor cur_sample isSelect empid from employee where grade > 4;

Beginopen cur_sample;loopfetch cur_sample into v_empid;exit when cur_sample%notfound; update employee

set salary = salary + 500where empid = v_empid;

end loop;End;

Open cursor for use.

Loops round each value

returned by the cursor

Place the value from the cursor into the variable v_empid

Stop when not more records are found

25463

12245

55983

12524

98543

Data returned by cursor

Declare Cursor

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Notepad file called:

Create_procedure.sql

1) Open SQL*Plus and logon

2) At the prompt enter:

@create_procedure

You will get a prompt which should say ‘procedure created’

3) To run the procedure enter:

Execute proc_test

4) If you check your data you should now find that the procedure has run successfully

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Use of conditions If statements can be used

If <condition> Then…..

End if;

Example

Remember to end the if statement and use of indented code will make it easier to debug!

. . .IF v_ename = 'MILLER' THEN v_job := 'SALESMAN'; v_deptno := 35; v_new_comm := sal * 0.20; END IF;. . .

. . .IF v_ename = 'MILLER' THEN v_job := 'SALESMAN'; v_deptno := 35; v_new_comm := sal * 0.20; END IF;. . .

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The %ISOPEN Attribute Fetch rows only when the cursor is open. Use the %ISOPEN cursor attribute before

performing a fetch to test whether the cursor is open.

Example

IF NOT cur_sample%ISOPEN THENOPEN cur_sample;

END IF;LOOP FETCH cur_sample...

IF NOT cur_sample%ISOPEN THENOPEN cur_sample;

END IF;LOOP FETCH cur_sample...

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DECLARE CURSOR emp_cursor IS SELECT empno, ename FROM emp; emp_record emp_cursor%ROWTYPE;BEGIN OPEN emp_cursor; LOOP FETCH emp_cursor INTO emp_record; ...

DECLARE CURSOR emp_cursor IS SELECT empno, ename FROM emp; emp_record emp_cursor%ROWTYPE;BEGIN OPEN emp_cursor; LOOP FETCH emp_cursor INTO emp_record; ...

Cursors and RecordsCursors and Records Process the rows of the active set conveniently by fetching values into a PL/SQL RECORD. Example

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Cursor FOR LoopsCursor FOR Loops

FOR record_name IN cursor_name LOOP

statement1;

statement2;

. . .

END LOOP;

FOR record_name IN cursor_name LOOP

statement1;

statement2;

. . .

END LOOP;

Syntax

The cursor FOR loop is a shortcut to process cursors.Implicitly opens, fetches, and closes cursor.The record is implicitly declared.

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Cursor FOR Loops: An ExampleCursor FOR Loops: An Example Retrieve employees one by one until no more are Retrieve employees one by one until no more are left.left. ExampleExample

DECLARE CURSOR emp_cursor IS SELECT ename, deptno FROM emp;BEGIN FOR emp_record IN emp_cursor LOOP -- implicit open and implicit fetch occur IF emp_record.deptno = 30 THEN ... END LOOP; -- implicit close occursEND;

DECLARE CURSOR emp_cursor IS SELECT ename, deptno FROM emp;BEGIN FOR emp_record IN emp_cursor LOOP -- implicit open and implicit fetch occur IF emp_record.deptno = 30 THEN ... END LOOP; -- implicit close occursEND;

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Seminar exercise The purpose of this exercise is to create a procedure which, when

evoked, will increase the salary of a grade by £500 or £1000 depending on the level of the grade. You will need to populate the table first with a minimum of 10 entries, the empgrade value should be between 1 and 5, and the idea is the higher the grade the higher the manager. There is a script for this on the BlackBoard/homepage.

Once you have done this you should compile the code this will then indicate if the procedure has compiled or not. If compilation is unsuccessful entering the command show errors will list any problems with the code. To run the procedure you type execute <procedure name> at the SQL prompt.