MySQL IF语句如何在存储过程中使用？
MySQLIF语句在存储过程中实现了基本的条件构造。它的语法如下-
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，我们创建了以下存储过程，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_IF”的过程，该过程中包含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 //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_IF('Computers', @S_Course);
mysql> Select @S_Course;
+-------------+
| @S_Course |
+-------------+
| B.Tech(CSE) |
+-------------+
1 row in set (0.00 sec)