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 STRUCTURE DECLARE (optional) - variable declarations BEGIN (required) - SQL statements - PL/SQL statements or sub-blocks EXCEPTION (optional) - actions to perform when errors occur END; (required) Comments  Enclosed within /* and */ for several lines’ comments  -- for single line comments

6 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 Variables 1. Scalar (char, varchar2, number, date, etc) 2. Composite (%rowtype) 3. Reference (pointers) 4. LOB (large objects)

9 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 directly var_emp_id:= ‘E101’ var_salary := 85100;  Assigning from the database, using SELECT query SELECT emp_salary INTO var_salary FROM employee WHERE emp_id = var_emp_id;

11 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) ARRAYARRAY

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; BEGIN l_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 5 th 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; /

17 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

20 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

DECLARE g_inv_value number(2); v_price number(8,2) := 10.25; v_quantitynumber(8,0) := 400; BEGIN g_inv_value := v_price * v_quantity; END; / Print g_inv_value /

PL/SQL Sample Program Set serveroutput on DECLARE v_inv_value number(10,2); v_price number(8,2) := 10.25; v_quantitynumber(8,0) := 400; BEGIN v_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 raise END; -- end of program

CONDITIONAL STATEMENTS IN PL/SQL

PL/SQL Control Structures  Conditional Control  Using IF and CASE statements DECLARE 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 > THEN l_bonus := 1500; ELSIF l_sales > 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 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 > LOOP l_i := l_i + 1; > 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 row Select 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

Cursors To 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

34 Declaring the Cursor DECLARE CURSOR low_pay IS SELECT surname,salary FROM Personnel where salary < 12000; v_surnamepersonnel.surname%TYPE; v_salarypersonnel.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 Cursor DECLARE var rows number(5); BEGIN UPDATE employee SET salary = salary ; IF SQL%NOTFOUND THEN dbms_output.put_line('None of the salaries were updated'); ELSIF SQL%FOUND THEN var_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 IS ; 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.

Syntax DECLARE 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 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 block BEGIN greetings; END; /

Deleting a Standalone Procedure  DROP PROcedure BEGIN DROP PROCEDURE greetings; END;

Parameter Modes in PL/SQL Subprograms 1. 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   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 function DECLARE 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 statement SELECT 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

Triggers Triggers 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   