Tạo stored procedure MySQL với tham số OUT

Bảng student_info:

mysql> SELECT * FROM student_info;
+------+---------+------------+------------+
| id   | Name    | Address    | Subject    |
+------+---------+------------+------------+
| 101  | YashPal | Amritsar   | History    |
| 105  | Gaurav  | Jaipur     | Literature |
| 110  | Rahul   | Chandigarh | History    |
| 125  | Raman   | Shimla     | Computers  |
+------+---------+------------+------------+
4 rows in set (0.00 sec)

Tạo procedure subjects đếm số lượng môn học: IN S_Subject, OUT total.

mysql> DELIMITER //
mysql> CREATE PROCEDURE subjects (IN S_Subject VARCHAR(25), OUT total INT)
    -> BEGIN
    -> SELECT COUNT(subject) INTO total
    -> FROM student_info
    -> WHERE subject = S_Subject;
    -> END //
Query OK, 0 rows affected (0.00 sec)
mysql> DELIMITER ;

Gọi procedure:

mysql> CALL subjects('Computers', @total); SELECT @total;  -- 1
mysql> CALL subjects('History', @total); SELECT @total;   -- 2