MySQL IF ELSE 语句如何在存储过程中使用？

MySQL IF ELSE 语句在表达式计算结果为 false 时实现基本条件构造。其语法如下 -

IF expression THEN statements; ELSE else-statements; END IF;登录后复制

为了演示在 MySQL 存储过程中使用 IF ELSE 语句，我们创建了以下存储过程：基于名为“student_info”的表的值，如下所示 -

mysql> Select * from student_info; +------+---------+------------+------------+ | id | Name | Address | Subject | +------+---------+------------+------------+ | 101 | YashPal | Amritsar | History | | 105 | Gaurav | Jaipur | Literature | | 125 | Raman | Shimla | Computers | +------+---------+------------+------------+ 3 rows in set (0.00 sec)登录后复制

mysql> DELIMITER // ; mysql> CREATE PROCEDURE coursedetails_IFELSE(IN S_Subject Varchar(20), OUT S_Course varchar(50)) -> BEGIN -> DECLARE Sub Varchar(20); -> SELECT Subject INTO SUB -> FROM Student_info WHERE S_Subject = Subject; -> IF Sub = 'Computers' THEN -> SET S_Course = 'B.Tech(CSE)'; -> ELSE -> SET S_Course = 'Subject Not in the table '; -> END IF; -> END // Query OK, 0 rows affected (0.00 sec)登录后复制

mysql> Delimiter ; // mysql> CALL coursedetails_IFELSE('Computers', @S_Course); Query OK, 1 row affected (0.00 sec) mysql> Select @S_Course; +-------------+ | @S_Course | +-------------+ | B.Tech(CSE) | +-------------+ 1 row in set (0.00 sec) mysql> CALL coursedetails_IFELSE ('History', @S_Course); Query OK, 0 rows affected (0.00 sec) mysql> Select @S_Course; +--------------------------------+ | @S_Course | +--------------------------------+ | Subject Not in the table | +--------------------------------+ 1 row in set (0.00 sec)登录后复制