Oracle9i Developer: PL/SQL Programming Chapter 3 PL/SQL Processing

Chapter Objectives Use control structures to make decisions Use looping structures to repeat code Work with the GOTO statement Manage errors with exception handlers Address exception-handling issues, such as RAISE_APPLICATION_ERROR and propagation Document code with comments

Brewbean’s Challenge

Control Structures IF Statements CASE Statements Basic IF IF/THEN/ELSE IF/THEN/ELSIF/ELSE CASE Statements Basic CASE statement Searched CASE statement CASE expression

Simple IF Statement

Add the ELSE clause

Add ELSIF clauses

NOT ELSEIF

Can check multiple conditions IF rec_order.state IN ('VA','PA','ME') THEN lv_tax_num := rec_order.sub * .06; ELSE lv_tax_num := rec_order.sub * .04; END IF;

Basic CASE Statement

No CASE Found Error

Searched CASE Statement

CASE Expression

Basic Loop

WHILE Loop

FOR Loop

Use Variables in FOR Loop DECLARE lv_upper_num NUMBER(3); BEGIN SELECT COUNT(idBasket) INTO lv_upper_num FROM bb_basket; FOR i IN 1..lv_upper_num LOOP DBMS_OUTPUT.PUT_LINE(i); END LOOP; END;

Reverse Option in FOR Loop Instructs counter to start with the upper bound value and increment by –1 to the lower bound value Example: FOR I IN REVERSE 1..5 LOOP

GOTO Statement Jumping control that instructs the program to move to another area of code to continue processing Most developers discourage the use of GOTO as it complicates the flow of execution

Exception Handlers Used to capture error conditions and handle the processing to allow the application to continue Placed in the EXCEPTION section of a PL/SQL block Two types of errors: Oracle errors (Predefined and Non-Predefined) User-defined errors RAISE_APPLICATION_ERROR

Predefined Oracle Errors Exception Name Description NO_DATA_FOUND A SELECT statement in a PL/SQL block retrieves no rows or a nonexistent row of an index-by table is referenced. TOO_MANY_ROWS A SELECT statement in a PL/SQL block retrieves more than one row. CASE_NOT_FOUND No WHEN clause in the CASE statement is processed. ZERO_DIVIDE Attempted division by zero. DUP_VAL_ON_INDEX Attempted violation of a unique or primary key column constraint.

Predefined Error Example

Add Exception Handler

Non-Predefined Handler Declare an exception Associate an Oracle error number to the exception name Foreign key error occurs if item lines are still in the bb_basketitem table Exception handler executes if Foreign key error –2292 is raised by the DELETE

User-Defined Exception Declare an exception If no rows updated, raise the exception Exception handler

Additional Exception Concepts WHEN OTHERS – traps all errors not specifically addressed by an exception handler and used for handling unanticipated errors SQLCODE and SQLERRM – Functions used to identify the error code and message especially in application testing to identify unanticipated errors

SQLCODE and SQLERRM Log error information to a database table using these functions

RAISE_APPLICATION_ERROR Allows developers to associate their own error number and message to an error Can only be used with stored programs which is covered in Chapter 4

Exception Propagation When an error occurs in a block, processing immediately moves to the EXCEPTION section of the block If the block is nested, and no handlers address the error, the processing will then move to the EXCEPTION section of the enclosing block

Commenting Code Add comments within code to identify code purpose and processing steps Use /* */ to enclose a multiline comment Use -- to add a single or partial line comment

Comment Examples DECLARE ex_prod_update EXCEPTION; --For UPDATE of no rows exception BEGIN /* This block is used to update product descriptions Constructed to support the Prod_desc.frm app screen Exception raised if no rows updated */ UPDATE bb_product SET description = 'Mill grinder with 5 grind settings!' WHERE idProduct = 30; --Check if any rows updated IF SQL%NOTFOUND THEN RAISE ex_prod_update; END IF; EXCEPTION WHEN ex_prod_update THEN DBMS_OUTPUT.PUT_LINE('Invalid product id entered'); END;

Summary Add conditional logic using IF and CASE statements Repeat lines of code using Loop structures Add error handlers in the EXCEPTION area to manage Oracle and user-defined errors Use comments in code for documentation