Chapter 16 Cursors and Exceptions

Chapter Objectives  Determine when an explicit cursor is required  Declare, open, and close an explicit cursor  Fetch data from an explicit cursor  Identify attributes associated with a cursor  Determine when an explicit cursor is required  Declare, open, and close an explicit cursor  Fetch data from an explicit cursor  Identify attributes associated with a cursor

Chapter Objectives  Use a cursor FOR loop to retrieve data from a cursor  Declare a cursor in the subquery of a cursor FOR loop  Evaluate BOOLEAN conditions combined with logical operators  Identify the purpose of the exception- handling section of a PL/SQL block  Use a cursor FOR loop to retrieve data from a cursor  Declare a cursor in the subquery of a cursor FOR loop  Evaluate BOOLEAN conditions combined with logical operators  Identify the purpose of the exception- handling section of a PL/SQL block

Chapter Objectives  Trap predefined exceptions in a PL/SQL block  Trap user-defined exceptions in a PL/SQL block  Trap predefined exceptions in a PL/SQL block  Trap user-defined exceptions in a PL/SQL block

Cursor  An area in memory that holds the values currently being processed  Must be explicitly declared when retrieving more than one row  An area in memory that holds the values currently being processed  Must be explicitly declared when retrieving more than one row

Opening an Explicit Cursor When opened, the memory is allocated, the SELECT statement is executed, and necessary data is loaded into the cursor

Closing the Cursor

Fetching Data from the Cursor  Data is retrieved from an explicit cursor using the FETCH command  Assigns the values to previously declared variables  Data is retrieved from an explicit cursor using the FETCH command  Assigns the values to previously declared variables

Cursor Attributes

Cursor Example Declaring a cursor Opening a cursor Fetching data Closing a cursor

Cursor FOR Loop Automatically opens and closes a cursor, and fetchs data from a cursor

Example Cursor FOR Loop

%ROWTYPE Attribute Specifies that a record will have the same structure as the row being retrieved

Logic Table Determines how a statement will be evaluated when conditions are joined with logical operators

Exception Handling  Exception – signal that an error has occurred  Does not include syntax errors  Common examples – NO_DATA_FOUND, TOO_MANY_ROWS, ZERO_DIVIDE  Exception – signal that an error has occurred  Does not include syntax errors  Common examples – NO_DATA_FOUND, TOO_MANY_ROWS, ZERO_DIVIDE

Exception-Handling Section Syntax

Exception Example

User-Defined Exception Handling  Name of exception must be declared with datatype EXCEPTION  Declared exception must be associated with Oracle server error number using PRAGMA EXCEPTION_INIT statement  Must be included in the block’s exception-handling section  Name of exception must be declared with datatype EXCEPTION  Declared exception must be associated with Oracle server error number using PRAGMA EXCEPTION_INIT statement  Must be included in the block’s exception-handling section

Syntax for the PRAGMA EXCEPTION_INIT Statement

Example of Trapping a User-Defined Exception