Chapter 15 Introduction to PL/SQL

Chapter Objectives  Explain the benefits of using PL/SQL blocks versus several SQL statements  Identify the sections of a PL/SQL block and describe their contents  Identify the mandatory and optional sections of a PL/SQL block  Identify an anonymous block and its use  Explain the benefits of using PL/SQL blocks versus several SQL statements  Identify the sections of a PL/SQL block and describe their contents  Identify the mandatory and optional sections of a PL/SQL block  Identify an anonymous block and its use

Chapter Objectives  Describe how to execute a PL/SQL block  Explain the purpose of a variable  Explain the difference between a constant and a variable  Identify valid variable names  List the valid datatypes for PL/SQL variables  Describe how to execute a PL/SQL block  Explain the purpose of a variable  Explain the difference between a constant and a variable  Identify valid variable names  List the valid datatypes for PL/SQL variables

Chapter Objectives  Assign a dynamic datatype for a PL/SQL variable  Initialize a PL/SQL variable  Use DML statements in a PL/SQL block  Determine when it is appropriate to use an IF statement  Identify all the clauses of an IF statement, and state when they should be used  Assign a dynamic datatype for a PL/SQL variable  Initialize a PL/SQL variable  Use DML statements in a PL/SQL block  Determine when it is appropriate to use an IF statement  Identify all the clauses of an IF statement, and state when they should be used

Chapter Objectives  Create an IF statement  Identify the purpose of a loop, and name the types of loops available in Oracle9i  Create a basic loop  Create a FOR loop  Create a WHILE loop  Create an IF statement  Identify the purpose of a loop, and name the types of loops available in Oracle9i  Create a basic loop  Create a FOR loop  Create a WHILE loop

PL/SQL  Procedure Language SQL  Advanced 4 th generation programming language  Procedure Language SQL  Advanced 4 th generation programming language

Advantages of PL/SQL  Can include error handling and control structures  Can be stored and used by various application programs or users  Allows for tighter security by granting privileges for executing stored procedures rather than directly on database object  Can include error handling and control structures  Can be stored and used by various application programs or users  Allows for tighter security by granting privileges for executing stored procedures rather than directly on database object

Types of Blocks  Function  Procedure  Anonymous block  Function  Procedure  Anonymous block

Function  Named block that is stored on the Oracle9i server  Accepts zero or more input parameters  Returns one value  Named block that is stored on the Oracle9i server  Accepts zero or more input parameters  Returns one value

Procedure  Named block  Can process several variables  Returns no values  Interacts with application program using IN, OUT, or INOUT parameters  Named block  Can process several variables  Returns no values  Interacts with application program using IN, OUT, or INOUT parameters

Anonymous Block  Not stored since it cannot be referenced by a name  Usually embedded in an application program, stored in a script file, or manually entered when needed  Not stored since it cannot be referenced by a name  Usually embedded in an application program, stored in a script file, or manually entered when needed

Basic Structure of a Block  Has three sections: –Declarative –Executable –Exception-handling  Executable section is the only required section; the rest are optional  Has three sections: –Declarative –Executable –Exception-handling  Executable section is the only required section; the rest are optional

Declarative Section  Identified by the DECLARE keyword  Used to define variables and constants referenced in the block  Forward execution – variable and constants must be declared before they can be referenced  Identified by the DECLARE keyword  Used to define variables and constants referenced in the block  Forward execution – variable and constants must be declared before they can be referenced

Executable Section  Identified by the BEGIN keyword  Mandatory  Can consist of several SQL and/or PL/SQL statements  Identified by the BEGIN keyword  Mandatory  Can consist of several SQL and/or PL/SQL statements

Exception-handling Section  Identified by the EXCEPTION keyword  Used to display messages or identify other actions to be taken when an error occurs  Addresses errors that occur during a statement’s execution  Identified by the EXCEPTION keyword  Used to display messages or identify other actions to be taken when an error occurs  Addresses errors that occur during a statement’s execution

END Keyword  Used to close a PL/SQL block  Always followed by a semicolon  Used to close a PL/SQL block  Always followed by a semicolon

Example PL/SQL Block

Declaring a Variable  Reserves a temporary storage area in the computer’s memory  Every variable must have: –A name –A datatype  Variables can be initialized  Reserves a temporary storage area in the computer’s memory  Every variable must have: –A name –A datatype  Variables can be initialized

Variable Names  Variable name can consist of up to 30 characters, numbers, or special symbols  Variable name must begin with a character  Variable name can consist of up to 30 characters, numbers, or special symbols  Variable name must begin with a character

Constants  Variables that have a value that does not change during the execution of the block  Optional CONSTANT keyword can be used to designate a constant in the block’s declarative section  Variables that have a value that does not change during the execution of the block  Optional CONSTANT keyword can be used to designate a constant in the block’s declarative section

PL/SQL Datatypes  Scalar – holds a single value  Composite – collection of grouped data treated as one unit  Reference – holds pointers to other program items  Large Object (LOB) – holds location of large objects  Scalar – holds a single value  Composite – collection of grouped data treated as one unit  Reference – holds pointers to other program items  Large Object (LOB) – holds location of large objects

PL/SQL Scalar Datatypes

Variable Initialization  Use DEFAULT keyword or (:=) assignment operator  Variable must be initialized if it is assigned a NOT NULL constraint  Use DEFAULT keyword or (:=) assignment operator  Variable must be initialized if it is assigned a NOT NULL constraint

Variable Initialization Examples

SELECT Statement Requires use of INTO clause to identify variable assigned to each data element

SELECT Statement Example

Cursors  Implicit cursor – created for DML operations or a SELECT statement that retrieves only one row of results  Explicit cursor – required for SELECT statements retrieving more than one row of results  Implicit cursor – created for DML operations or a SELECT statement that retrieves only one row of results  Explicit cursor – required for SELECT statements retrieving more than one row of results

Execution Control  IF statement – executes statements based on a condition  Basic loop – executes statements until condition in EXIT clause is TRUE  FOR loop – uses counter  WHILE loop – executes statements until condition is FALSE  IF statement – executes statements based on a condition  Basic loop – executes statements until condition in EXIT clause is TRUE  FOR loop – uses counter  WHILE loop – executes statements until condition is FALSE

IF Statement Syntax

IF Statement Example

Basic Loop Syntax

Basic Loop Example

FOR Loop Syntax

FOR Loop Example

WHILE Loop Syntax

WHILE Loop Example

Nested Loops  Any type of loop can be nested inside another loop  Execution of the inner loop must be completed before control is returned to the outer loop  Any type of loop can be nested inside another loop  Execution of the inner loop must be completed before control is returned to the outer loop

Nested Loop Example