示例：使用 IF 语句

    1. CREATE OR REPLACE PROCEDURE sp_guess(p_value IN number)
    2. IS
    3. BEGIN
    4.     IF p_value IS NULL THEN
    5.         dbms_output.put_line('The value is NULL!');
    6.     ELSIF (p_value < 0) THEN
    7.         dbms_output.put_line('The value is a negative number. ');
    8.     ELSE 
    9.     END IF; 
    10. END;
    11. /
    13. delimiter ;
    15. obclient>
    16. obclient> set serveroutput on;
    18. obclient> call sp_guess(2020);
    19. Query OK, 0 rows affected (0.03 sec)
    21. The value is a positive number.
    22. obclient> call sp_guess(-2000);
    23. Query OK, 0 rows affected (0.00 sec)
    25. obclient>