MySQL IF ELSE语句如何在存储过程中使用？
当表达式的计算结果为false时，MySQL IFELSE语句实现基本的条件构造。它的语法如下-
IF expression THEN statements; ELSE else-statements; END IF;
语句必须以分号结尾。
为了演示IFELSE 语句在MySQL存储过程中的使用，我们正在创建以下存储过程，该存储过程基于如下所示的名为“student_info”的表的值-
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)
以下查询将创建一个名为“coursedetails_IFELSE”的过程，其中包含IFELSE语句-
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 //
现在，当我们调用此过程时，我们可以看到以下结果：
mysql> Delimiter ; //
mysql> CALL coursedetails_IFELSE('Computers', @S_Course);
mysql> Select @S_Course;
+-------------+
| @S_Course |
+-------------+
| B.Tech(CSE) |
+-------------+
1 row in set (0.00 sec)
mysql> CALL coursedetails_IFELSE ('History', @S_Course);
mysql> Select @S_Course;
+--------------------------------+
| @S_Course |
+--------------------------------+
| Subject Not in the table |
+--------------------------------+
1 row in set (0.00 sec)