如何使用OUT参数创建MySQL存储过程？
为了使其理解，我们使用名为“student_info”的表，该表具有以下值-
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)
现在，借助以下查询，我们将创建一个带有OUT参数的存储过程，该存储过程将通过提供主题名称作为参数来计算特定主题的总数。
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 // mysql> DELIMITER ;
“S-Subject”是IN参数，它是我们要计算的主题数，“total”是OUT参数，用于存储特定主题的主题数。
mysql> CALL subjects('Computers', @total);
mysql> Select @total;
+--------+
| @total |
+--------+
| 1 |
+--------+
1 row in set (0.01 sec)
mysql> CALL subjects('History', @total);
mysql> Select @total;
+--------+
| @total |
+--------+
| 2 |
+--------+
1 row in set (0.00 sec)