Conditions

Decision-making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Statement	Description
IF - THEN statement	The IF statement associates a condition with a sequence of statements enclosed by the keywords THEN and END IF. If the condition is true, the statements get executed and if the condition is false or NULL then the IF statement does nothing.
IF-THEN-ELSE statement	IF statement adds the keyword ELSE followed by an alternative sequence of statement. If the condition is false or NULL , then only the alternative sequence of statements get executed. It ensures that either of the sequence of statements is executed.
IF-THEN-ELSIF statement	It allows you to choose between several alternatives.
Case statement	Like the IF statement, the CASE statement selects one sequence of statements to execute. However, to select the sequence, the CASE statement uses a selector rather than multiple Boolean expressions. A selector is an expression whose value is used to select one of several alternatives.
Searched CASE statement	The searched CASE statement has no selector, and it's WHEN clauses contain search conditions that yield Boolean values.
nested IF-THEN-ELSE	You can use one IF-THEN or IF-THEN-ELSIFstatement inside another IF-THEN or IF-THEN-ELSIF statement(s).

Example 1:

   a   NUMBER (2) := 10;

BEGIN

   a := 10;                  -- check the boolean condition using if statement

   IF (a < 20)

   THEN                       -- if condition is true then print the following

      DBMS_OUTPUT.put_line ('a is less than 20 ');

   END IF;

   DBMS_OUTPUT.put_line ('value of a is : ' || a);

END;

Example 2:

DECLARE

a number(3) := 100;

BEGIN

-- check the boolean condition using if statement

IF( a < 20 ) THEN

-- if condition is true then print the following

dbms_output.put_line('a is less than 20 ' );

ELSE

dbms_output.put_line('a is not less than 20 ' );

END IF;

dbms_output.put_line('value of a is : ' || a);

END;

Example 3:

DECLARE

   a   NUMBER (3) := 100;

BEGIN

   IF (a = 10)

   THEN

      DBMS_OUTPUT.put_line ('Value of a is 10');

   ELSIF (a = 20)

   THEN

      DBMS_OUTPUT.put_line ('Value of a is 20');

   ELSIF (a = 30)

   THEN

      DBMS_OUTPUT.put_line ('Value of a is 30');

   ELSE

      DBMS_OUTPUT.put_line ('None of the values is matching');

   END IF;

    DBMS_OUTPUT.put_line ('Exact value of a is: ' || a);

END;


Example 4:

DECLARE

   a   NUMBER (3) := 100;

   b   NUMBER (3) := 200;

BEGIN

   -- check the boolean condition

   IF (a = 100)

   THEN

      -- if condition is true then check the following

      IF (b = 200)

      THEN

         -- if condition is true then print the following

         DBMS_OUTPUT.put_line ('Value of a is 100 and b is 200');

      END IF;

   END IF;

   DBMS_OUTPUT.put_line ('Exact value of a is : ' || a);

   DBMS_OUTPUT.put_line ('Exact value of b is : ' || b);

END;

GOTO statement: A GOTO statement in PL/SQL programming language provides an unconditional jump from the GOTO to a labeled statement in the same subprogram.

DECLARE

   a   NUMBER (2) := 10;

BEGIN

  <<loopstart>>

   -- while loop execution

   WHILE a < 20

   LOOP

      DBMS_OUTPUT.put_line ('value of a: ' || a);

      a := a + 1;

      IF a = 15

      THEN

         a := a + 1;

         GOTO loopstart;

      END IF;

   END LOOP;

END;