MySQL IF 语句在存储过程中实现基本条件构造。其语法如下 -
IF expression THEN
Statements;
END IF;它必须以分号结尾。为了演示 IF 语句在 MySQL 存储过程中的使用，我们将创建以下存储过程，该过程基于名为“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)以下查询将创建一个名为“coursedetails_IF”的过程，其中包含 IF 语句 -
mysql> DELIMITER // ;
mysql> CREATE PROCEDURE coursedetails_IF(IN S_Subject Varchar(20), OUT S_Course varchar(20))
-> 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)';
-> END IF;
-> END //
Query OK, 0 rows affected (0.00 sec)现在，当我们调用这个过程时，我们可以看到下面的结果 -
mysql> Delimiter ; //
mysql> CALL coursedetails_IF('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)
