PL/SQL

What is PL/SQL Procedural Language – SQL An extension to SQL with design features

of programming languages (procedural and object oriented)

PL/SQL and Java are both supported as internal host languages within Oracle products.

Why PL/SQL Acts as host language for stored procedures

and triggers. Provides the ability to add middle tier business

logic to client/server applications. Provides Portability of code from one

environment to another Improves performance of multi-query

transactions. Provides error handling Full-featured programming language Interpreted language

PL/SQL BLOCK STRUCTUREDECLARE (optional)

- variable declarationsBEGIN (required)

- SQL statements - PL/SQL statements or sub-blocksEXCEPTION (optional)

- actions to perform when errors occurEND; (required)

Comments Enclosed within /* and */ for several lines’ comments -- for single line comments

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PL/SQL Variables and Data Types

Variable names must follow the Oracle naming standard (Example: current_s_id, not $current_s_id)

Strongly typed language All variables must be declared before their use. The assignment statement : = is not the same as the

equality operator = All statements end with a ;

Variable declaration syntax:variable_name data_type_declaration;

Default value always NULL

Variable Naming Conventions Two variables can have the same name

if they are in different blocks (bad idea) The variable name should not be the

same as any table column names used in the block.

PL/SQL Variables1. Scalar (char, varchar2, number, date,

etc)2. Composite (%rowtype)3. Reference (pointers)4. LOB (large objects)

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1. Scalar Variables Reference single value such as number, date, string Data types correspond to Oracle 10g database data

types VARCHAR2 CHAR DATE NUMBER

Assigning a value to a variable

Assigning directlyvar_emp_id:= ‘E101’var_salary := 85100;  

Assigning from the database, using SELECT querySELECT emp_salary

INTO var_salary FROM employee WHERE emp_id = var_emp_id;  

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2. Composite Variables

Data object made up of multiple individual data elements

Data structure contains multiple scalar variables Composite variable data types include:

RECORD (multiple scalar values similar to a table’s record) TABLE (tabular structure with multiple columns and rows) VARRAY (variable-sized array. Tabular structure that can

expand or contract based on data values)

ARRAY

Placeholders Placeholders are temporary storage

area. PL/SQL Placeholders can be any of

Variables, Constants and Records. Oracle defines placeholders to store data

temporarily, which are used to manipulate data during the execution of a PL SQL block.

PL/SQL placeholders Scalar type

variable constant

Single composite/vector type Record

Used for reading rows from table Can contain multiple types of data

Collections Associative Array Variable-sized Array (VARRAY) Nested Tables

TYPE T_TIME IS RECORD (minutes INTEGER, hours NUMBER(2));current_time_rec T_TIME;Current_time_rec.hours := 12;

PL/SQL placeholders DECLARE

TYPE T_POPULATION IS TABLE OF NUMBER INDEX BY VARCHAR2(64);l_city_population T_POPULATION;l_i number;

BEGINl_city_population('Smallville') := 2000;l_i:= l_city_population('Smallville') ;

END; /

PL/SQL placeholders DECLARE

TYPE T_FOURSOME IS VARRAY(4) OF VARCHAR2(15); l_team T_FOURSOME := T_FOURSOME('John', 'Mary', 'Alberto');

BEGIN l_team.EXTEND; -- Append one null element

l_team(4):='Mike'; -- Set 5th element element DBMS_OUTPUT.PUT_LINE( l_team( l_team.first ) ); -- Print first element

DBMS_OUTPUT.PUT_LINE( l_team( l_team.last ) ); -- Print last element

END; /

PL/SQL placeholders DECLARE

TYPE T_ROSTER IS TABLE OF VARCHAR2(15);l_names T_ROSTER := T_ROSTER('D Caruso', 'J Hamil', 'D Piro', 'R Singh');

l_i number;BEGIN

FOR l_i IN l_names.FIRST .. L_names.LAST LOOP --For first to last element DBMS_OUTPUT.PUT_LINE(l_names(l_i)); END LOOP; END; /

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3. Reference Variables

Directly reference specific database column or row Assume data type of associated column or row

%TYPE data declaration syntax: variable_name tablename.fieldname%TYPE; %ROWTYPE data declaration syntax: variable_name tablename%ROWTYPE;

Attributes %TYPE & %ROWTYPE %TYPE references type of a variable or a

database column %ROWTYPE references type of a record

structure, table row or a cursor Advantages:

Actual type does not need to be known referenced type had changed -> will be

recompiled automatically

%TYPE & %ROWTYPE Examples

balance NUMBER(7,2);

minimum_balance balance%TYPE := 10.00;

my_dname scott.dept.dname%TYPE;

dept_rec dept%ROWTYPE;

SELECT deptno, dname, loc INTO dept_rec FROM dept WHERE deptno = 30;

variable declarations

using record variable to read a row from a table

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Writing a PL/SQL Program

1. Write PL/SQL program in Notepad or another text editor

2. Copy and paste program commands from text editor into SQL*Plus

3. Press Enter after last program command

4. Type front slash ( / )5. Then press Enter again

PL/SQL Sample Program

PL/SQL Sample ProgramDECLARE g_inv_value number(2);v_price number(8,2) := 10.25;

v_quantity number(8,0) := 400;BEGINg_inv_value := v_price * v_quantity;

END;/Print g_inv_value/

PL/SQL Sample ProgramSet serveroutput onDECLARE v_inv_value number(10,2);v_price number(8,2) := 10.25;

v_quantity number(8,0) := 400;BEGINv_inv_value := v_price * v_quantity;

dbms_output.put('The value is: '); dbms_output.put_line(v_inv_value);END;/

PL/SQL Comments

DECLARE v_salary number(9,2) := 40000;BEGIN /* this is a multi-line comment that will be ignored by the pl/sql interpreter */ v_salary := v_salary * 2; -- nice raiseEND; -- end of program

CONDITIONAL STATEMENTS IN PL/SQL

PL/SQL Control Structures Conditional Control

Using IF and CASE statementsDECLARE

l_grade CHAR(1) := 'B'; BEGIN

CASE l_grade WHEN 'A' THEN

DBMS_OUTPUT.PUT_LINE('Excellent'); WHEN 'B' THEN DBMS_OUTPUT.PUT_LINE('Very

Good'); WHEN 'C' THEN DBMS_OUTPUT.PUT_LINE('Good'); WHEN 'D' THEN DBMS_OUTPUT.PUT_LINE('Fair'); WHEN 'F' THEN DBMS_OUTPUT.PUT_LINE('Poor'); ELSE DBMS_OUTPUT.PUT_LINE('No such grade');

END CASE; END;

DECLARE l_sales NUMBER(8,2) := 20000; l_bonus NUMBER(6,2);

BEGIN IF l_sales > 50000 THEN l_bonus := 1500; ELSIF l_sales > 35000 THEN l_bonus := 500;

ELSE l_bonus := 100; END IF; UPDATE employees SET salary = salary + l_bonus;

END;

PL/SQL Control Structures Iterative loops

Simple loop (infinite) WHILE loop FOR loop

Numeric range Reversed

Cursor based

DECLARE

l_i NUMBER := 0;

BEGIN

LOOP

DBMS_OUTPUT.PUT_LINE (TO_CHAR(l_i));

l_i:=l_i+1;

END LOOP;

WHILE l_i < 10 LOOP

DBMS_OUTPUT.PUT_LINE (TO_CHAR(l_i));

l_i := l_i + 1;

END LOOP;

FOR l_i IN 1..500 LOOP

DBMS_OUTPUT.PUT_LINE (TO_CHAR(l_i));

END LOOP;

FOR l_i IN REVERSE 1..3 LOOP DBMS_OUTPUT.PUT_LINE (TO_CHAR(l_i));

END LOOP;

END;

PL/SQL Control Structures

Oracle Tutorials: PL/SQL

Iterative loops Named loops

Exiting loops EXIT statement

Loop skipping CONTINUE

DECLARE

l_i NUMBER := 0;

l_j NUMBER := 0;

l_s NUMBER :=0;

BEGIN

<<outer_loop>>LOOP

l_i := l_i + 1;

<<inner_loop>>LOOP

l_j := l_j + 1;

l_s := l_s + l_i * l_j;

EXIT inner_loop WHEN (l_j > 5);

EXIT outer_loop WHEN ((l_i * l_j) > 15);

END LOOP inner_loop;DBMS_OUTPUT.PUT_LINE('Sum:'||TO_CHAR(l_s));

IF l_s > 100 THEN EXIT;

END IF;

END LOOP outer_loop;END;

Accessing Data in the Database Selecting at most one row:

SELECT INTO statement

Selecting Multiple rows: Cursors

Inserting and updating

SELECT COUNT(*) INTO variable FROM table;SELECT * INTO record FROM table WHERE …;

INSERT INTO table VALUES (var1, var2, …);

Remember the SELECT INTO…… ?

It only allowed the retrieval of one rowSelect attribute into variable from … where …

Or

Select count(*) into variable from ………

But when we want to retrieve multiple rows we need to use what is called a CURSOR

CursorsTo process an SQL statement, ORACLE

needs to create an area of memory known as the context area

Cursors A cursor is a temporary work area created in

the system memory when a SQL statement is executed

A cursor contains information on a select statement and the rows of data accessed by it.

This area is used to store the data retrieved from the database, and manipulate this data. A cursor can hold more than one row, but can process only one row at a time.

The set of rows the cursor holds is called the active set.

Cursor structure Declare it

This is achieved by a SELECT command And by giving the CURSOR a name

Open it Fetch row(s) from it Close it

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Declaring the Cursor

DECLARECURSOR low_pay

IS SELECT surname,salaryFROM Personnelwhere salary < 12000;

v_surname personnel.surname%TYPE;v_salary personnel.salary%TYPE;BEGIN…..

Because a cursor is associated with multiple rows they are normally used with LOOP structures

Types Of Cursors

An IMPLICIT cursor is automatically declared by Oracle every time an SQL statement is executed.

The user will not be aware of this happening and will not be able to control or process the information in an implicit cursor

An EXPLICIT cursor is defined by the program for any query that returns more than one row of data.

They must be created when you are executing a SELECT statement that returns more than one row. Even though the cursor stores multiple records, only one record can be processed at a time, which is called as current row. When you fetch a row the current row position moves to next row.

Implicit Cursors The cursor attributes available are %FOUND, %NOTFOUND,

%ROWCOUNT, and %ISOPEN.

Example-Implicit CursorDECLARE var rows number(5);BEGINUPDATE employee SET salary = salary + 1000;IF SQL%NOTFOUND THENdbms_output.put_line('None of the salaries were updated');ELSIF SQL%FOUND THENvar_rows := SQL%ROWCOUNT;dbms_output.put_line('Salaries for ' || var_rows || 'employees are updated');END IF; END; 

Implicit cursor

Explicit Cursor An explicit cursor is defined in the

declaration section of the PL/SQL Block. It is created on a SELECT Statement

which returns more than one row.

CURSOR <cursor_name> IS <select_statement>;

  cursor_name – A suitable name for the cursor.

select_statement – A select query which returns multiple rows.

How to use Explicit Cursor?

Four steps 1.  DECLARE the cursor in the declaration section.2. OPEN the cursor in the Execution Section.3. FETCH the data from cursor into PL/SQL variables or

records in the Execution Section.4. CLOSE the cursor in the Execution Section before you end

the PL/SQL Block.

SyntaxDECLARE

variables;records;declare a cursor;

BEGIN OPEN cursor;FETCH cursor;

process the records;CLOSE cursor;

END;

Example DECLARE emp_rec emp_tbl%rowtype; CURSOR emp_cur IS SELECT * FROM employee WHERE salary > 10; BEGIN OPEN emp_cur; FETCH emp_cur INTO emp_rec;

dbms_output.put_line (emp_rec.first_name || ' ' || emp_rec.last_name); CLOSE emp_cur;

END;

Using explicit cursors with loop

DECLARE CURSOR emp_cur IS SELECT first_name, last_name, salary FROM emp_tbl;

emp_rec emp_cur%rowtype; BEGIN

IF NOT sales_cur%ISOPEN THEN OPEN sales_cur;

END IF; LOOP

FETCH emp_cur INTO emp_rec; EXIT WHEN emp_cur%NOTFOUND;

dbms_output.put_line(emp_cur.first_name || ' ' ||emp_cur.last_name || ' ' ||emp_cur.salary); END LOOP;

END;

Procedures

A subprogram is a program unit/module that performs a particular task. These subprograms are combined to form larger programs. This is basically called the 'Modular design'. A subprogram can be invoked by another subprogram or program which is called the calling program.

A subprogram can be created: At schema level Inside a package Inside a PL/SQL block

PL/SQL subprograms are named PL/SQL blocks that can be invoked with a set of parameters. PL/SQL provides two kinds of subprograms: Functions: these subprograms return a single

value, mainly used to compute and return a value.

Procedures: these subprograms do not return a value directly, mainly used to perform an action.

Creating a Procedure

A procedure is created with the CREATE OR REPLACE PROCEDURE statement.

CREATE [OR REPLACE] PROCEDURE procedure_name [(parameter_name [IN | OUT | IN OUT] type [, ...])] {IS | AS} BEGIN < procedure_body > END procedure_name;

Where, procedure-name specifies the name of the procedure. [OR REPLACE] option allows modifying an existing

procedure. The optional parameter list contains name, mode and

types of the parameters. IN represents that value will be passed from outside and OUT represents that this parameter will be used to return a value outside of the procedure.

procedure-body contains the executable part. The AS keyword is used instead of the IS keyword for

creating a standalone procedure.

Example-1 CREATE OR REPLACE PROCEDURE

greetings AS BEGIN dbms_output.put_line('Hello World!'); END; /

Executing a Standalone Procedure A standalone procedure can be called in

two ways: Using the EXECUTE keyword

EXECUTE greetings; Calling the name of the procedure from a

PL/SQL blockBEGIN greetings; END; /

Deleting a Standalone Procedure DROP PROcedure

BEGIN DROP PROCEDURE greetings; END;

Parameter Modes in PL/SQL Subprograms1. IN-parameters - These types of parameters are

used to send values to stored procedures.2. OUT-parameters - These types of parameters are

used to get values from stored procedures.3. IN OUT-parameters - This is similar to a return type

in functions. These types of parameters are used to send values and get values from stored procedures.

NOTE: If a parameter is not explicitly defined a parameter type, then by default it is an IN type parameter.

Functions

Creating a function CREATE [OR REPLACE] FUNCTION

function_name [(parameter_name [IN | OUT | IN OUT] type [, ...])] RETURN return_datatype

{IS | AS} BEGIN < function_body > END [function_name];

function-name specifies the name of the function. [OR REPLACE] option allows modifying an existing function. The optional parameter list contains name, mode and types of the

parameters. IN represents that value will be passed from outside and OUT represents that this parameter will be used to return a value outside of the procedure.

The function must contain a return statement. RETURN clause specifies that data type you are going to return from the

function. function-body contains the executable part. The AS keyword is used instead of the IS keyword for creating a

standalone function.

CREATE OR REPLACE FUNCTION totalCustomers RETURN number IS total number(2) := 0; BEGIN SELECT count(*) into total FROM customers; RETURN total; END; /

It returns the total number of CUSTOMERS in the customers table.

Calling a functionDECLARE c number(2); BEGIN c := totalCustomers(); dbms_output.put_line('Total no. of

Customers: ' || c); END; /Output:Total no. of Customers: 6 PL/SQL procedure successfully completed.

How to execute a PL/SQL Function?1) Since a function returns a value we can assign it to a variable.employee_name := employer_details_func(); If ‘employee_name’ is of datatype varchar we can store the name of the

employee by assigning the return type of the function to it. 2) As a part of a SELECT statementSELECT employer_details_func FROM dual; 3) In a PL/SQL Statements like,dbms_output.put_line(employer_details_func); This line displays the value returned by the function.

Procedures vs Functions

TriggersTriggers are stored programs, which are automatically executed or

fired when some events occcur. Executed in response to any of the following events:

A database manipulation (DML) statement (DELETE, INSERT, or UPDATE). A database definition (DDL) statement (CREATE, ALTER, or DROP). A database operation (SERVERERROR, LOGON, LOGOFF, STARTUP, or

SHUTDOWN).

Note: Triggers could be defined on the table, view, schema, or database with which the event is associated.

Triggers can be written for the following purposes: Generating some derived column values automatically Enforcing referential integrity Event logging and storing information on table access Auditing Synchronous replication of tables Imposing security authorizations Preventing invalid transactions

Creating Triggers

CREATE [OR REPLACE] TRIGGER trigger_name: Creates or replaces an existing trigger with thetrigger_name.

{BEFORE | AFTER | INSTEAD OF} : This specifies when the trigger would be executed. The INSTEAD OF clause is used for creating trigger on a view.

{INSERT [OR] | UPDATE [OR] | DELETE}: This specifies the DML operation. [OF col_name]: This specifies the column name that would be updated. [ON table_name]: This specifies the name of the table associated with the trigger. [REFERENCING OLD AS o NEW AS n]: This allows you to refer new and old values for

various DML statements, like INSERT, UPDATE, and DELETE. [FOR EACH ROW]: This specifies a row level trigger, i.e., the trigger would be

executed for each row being affected. Otherwise the trigger will execute just once when the SQL statement is executed, which is called a table level trigger.

WHEN (condition): This provides a condition for rows for which the trigger would fire. This clause is valid only for row level triggers.

Example

Triggering a Trigger

References http://www.plsql-tutorial.com http://www.java2s.com/Tutorial/Oracle/ http://www.tutorialspoint.com/plsql