Program with PL/SQL

Lesson 4

Writing Control Structure

Controlling PL/SQL Flow of Execution

Change the logical execution of statements using conditional IF statements and loop control structures.

Conditional IF statements: IF – THEN – END IF IF – THEN – ELSE – END IF IF – THEN – ELSIF – END IF

CASE Expressions

A CASE expressions selects a result and returns it

To select the result. The CASE expressions uses an expression whose values is used to select one of several alternatives

CASE selector

WHEN expressions1 THEN result1

WHEN expressions2 THEN result2

…

WHEN expressionsN THEN resultN

[ELSE resultN+1;]

END;

declare vgrade char(1) := upper('&p_grade'); va varchar2(20);begin va := case vgrade when 'A' then 'Excellent' when 'B' then 'very good' when 'C' then 'Good' else 'no such grade' end; dbms_output.put_line('Grade: '||vgrade||'App'||va);end;

Handling Nulls

Simple comparison involving nulls always yield NULL

Applying the logical operator NOT to a null yields NULL

In conditional control statements, if the condition yields NULL, its associated sequence of statements is not executed

Logic Tables

AND TRUE FALSE NULL

TRUE TRUE FALSE NULL

FALSE FALSE FALSE FALSE

NULL NULL FALSE NULL

OR TRUE FALSE NULL

TRUE TRUE TRUE TRUE

FALSE TRUE FALSE NULL

NULL TRUE NULL NULL

NOT

TRUE FALSE

FALSE TRUE

NULL NULL

Iterative Control: LOOP Statements

Loops repeat a statement or sequence of statements multiple times

There are three loop types Basic loop FOR loop WHILE loop

Basic Loops

Syntax:

LOOP -- delimiter

Statement1; -- statements

...EXIT [WHEN condition]; -- EXIT statements

END LOOP -- delimiter

Contoh….

DECLARE ord_id order.order_id%type := 97; vcount number(2) := 0;BEGIN LOOP INSERT INTO order(order_id,item_id,product_id,actual_price) VALUES (ord_id,vcount,1011,0); vcount := vcount + 1; EXIT WHEN vcount > 10; END LOOP;END;/

WHILE Loops

Syntax:

WHILE condition LOOP

Statement1;

Statement2;

...END LOOP

Condition is evaluated at the beginning of each iteration

Use the WHILE loop to repeat statements while a condition is TRUE

Contoh…

DECLARE ord_id order.order_id%type := 97; vcount number(2) := 1;BEGIN WHILE vcount <= 10 LOOP INSERT INTO order(order_id,item_id,product_id,actual_price) VALUES (ord_id,vcount,1011,0); vcount := vcount + 1; END LOOP;END;/

FOR Loops

Syntax:FOR counter IN [REVERSE]

lower_bound .. Upper_bound LOOPStatement1;

Statement2;

...

END LOOP

Use a FOR loop to shortcut the test for the number of iterations

Do not declare the counter; it is declared implicitly ‘lower_bound .. Upper_bound’ is required syntax

Contoh…

DECLARE

ord_id order.order_id%type := 97;

BEGIN

FOR vcount IN 1..10 LOOP INSERT INTO order(order_id,item_id,product_id,actual_price)

VALUES (ord_id,vcount,1011,0);

END LOOP;

END;

/

FOR Loops

Guidelines Reference the counter within the loop only; it

is undefined outside the loop Do not reference the counter as the targert of

an assignment

Guidelines While Using Loops

Use the basic loop when the statements inside the loop must execute at least once

Use the WHILE loop if the condition has to be evaluated at the start of each iteration

Use a FOR loop if the number of iterations is known

Nested Loops and Labels

Nest loops to multiple levels

Use labels to distinguish between blocks and loops

Exit the outer loop with the EXIT statement that references the label

declare the_counter number(2) := 0; total_done varchar2(3) := 'NO'; inner_done varchar2(3) := 'NO';begin <<outer_loop>> loop exit when the_counter > 10; dbms_output.put_line('outer loop : the_counter = '||the_counter); the_counter := the_counter + 1; <<inner_loop>> loop exit inner_loop when inner_done = 'YES'; dbms_output.put_line('inner loop:the_counter= '|| the_counter); if the_counter = 5 then inner_done := 'YES'; dbms_output.put_line('will exit inner loop'); else the_counter := the_counter + 1; end if; end loop inner_loop; exit outer_loop when total_done = 'YES'; end loop outer_loop;end;

Practice Overview

Practice 1

Create a PL/SQL block that rewards an employee by appending an asterisk in the STARS column for every $1000 of the employee’s salary.

a. Use the DEFINE command to provide the employee_id. Pass the value to the PL/SQL block through a iSQL*Plus substitution variable

b. Initialize a v_asterisk variable that contains a NULLc. Append an asterisk to the string for every $1000 of the

salary amount. For example, if the employee has a salary amount $8000, the string of asterisk should contain eight asterisk. If the employee has a salary amount of $12500, the string of asterisks should contains 13 asterisks

d. Update the STARS column for the employee with the string of asterisk

e. COMMIT

Practice 2

In a loop, use a cursor to retrieve the department number and department name from the DEPARTMENTS table for those departments whose DEPARTMENT_ID is less than 100. Pass the department number to another cursor to retrieve from the EMPLOYEES table the details of employee last name, job, hire_date, and salary of those employees whose EMPLOYEE_ID is less than 120 and who work in that department.

Practice 3

In a loop use the iSQL*Plus substitution parameter created in step 1 and gather the salaries of the top n people from the EMPLOYEES table. There should be no duplication in the salaries. If two employees earn the same salary, the salary should be picked up only once and store the salaries in the TOP_DOGS table