PL/SQL编程嵌套if-else语句，可以使用一个IF或ELSE IF语句中的另一个IF或ELSE IF语句。

语法:

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;

示例:

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;
/

当上述代码在SQL提示符执行时，它产生了以下结果：

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.