PL/SQL - Nested IF-THEN-ELSE Statements

It is always legal in PL/SQL programming to nest the IF-ELSE statements, which means you can use one IF or ELSE IF statement inside another IF or ELSE IF statement(s).

Syntax

IF( boolean_expression 1)THEN 
   -- executes when the boolean expression 1 is true  
   IF(boolean_expression 2) THEN 
      -- executes when the boolean expression 2 is true  
      sequence-of-statements; 
   END IF; 
ELSE 
   -- executes when the boolean expression 1 is not true 
   else-statements; 
END IF; 

Example

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; 
/ 

When the above code is executed at the SQL prompt, it produces the following result −

Value of a is 100 and b is 200 
Exact value of a is : 100 
Exact value of b is : 200  

PL/SQL procedure successfully completed.