MySQL IF ELSEIF ELSE语句如何在存储过程中使用？
MySQL IFELSEIFELSE基于多个表达式执行语句。其语法如下-
IF expression THEN statements; ELSEIF elseif-expression THEN elseif-statements; … … … … ELSE else-statements; END IF;
语句必须以分号结尾。
为了演示IFELSEIFELSE语句在MySQL存储过程中的使用，我们基于以下名为“student_info”的表的值创建以下存储过程-
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_ELSEIF”的过程，该过程中包含IFELSEIFELSE语句-
mysql> DELIMITER // ;
mysql> CREATE PROCEDURE coursedetails_IF_ELSEIF(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)';
-> ELSEIF Sub = 'History' THEN
-> SET S_Course = 'Masters in History';
-> ELSEIF Sub = 'Literature' THEN
-> SET S_Course = 'Masters in English';
-> 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_ELSEIF('Computers', @S_Course);
mysql> Select @S_Course;
+-------------+
| @S_Course |
+-------------+
| B.Tech(CSE) |
+-------------+
1 row in set (0.00 sec)
mysql> CALL coursedetails_IF_ELSEIF ('Literature', @S_Course);
mysql> Select @S_Course;
+--------------------+
| @S_Course |
+--------------------+
| Masters in English |
+--------------------+
1 row in set (0.00 sec)