1. Program with PL/SQL
Lesson 4

2. Writing Control Structure

3. 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

4. IF Statements Syntax: IF condition THEN statements;
[ELSIF condition THEN
statements;]
[ELSE
END IF;

5. 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;

6. 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

7. Logic Tables
AND
TRUE
FALSE
NULL OR
TRUE
FALSE
NULL

8. 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

9. Basic Loops Syntax: LOOP -- delimiter Statement1; -- statements ...
EXIT [WHEN condition]; -- EXIT statements
END LOOP delimiter

10. 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

11. FOR Loops
Syntax:
FOR counter IN [REVERSE]
lower_bound .. Upper_bound LOOP Statement1;
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

12. 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

13. 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

14. 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

15. Practice Overview

16. 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.
Use the DEFINE command to provide the employee_id. Pass the value to the PL/SQL block through a iSQL*Plus substitution variable
Initialize a v_asterisk variable that contains a NULL
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
Update the STARS column for the employee with the string of asterisk
COMMIT

17. 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.

18. 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