使用WHEN子句实现MySQL CASE语句
带WHEN子句的CASE语句用于解决条件。以下是语法-
select *, case when yourCondition then yourStatement when yourCondition then yourStatement . . else yourStatement from yourTableName;
让我们首先创建一个表-
mysql> create table DemoTable -> ( -> StudentName varchar(20), -> StudentMarks int -> );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable values('Chris',78);
mysql> insert into DemoTable values('Robert',88);
mysql> insert into DemoTable values('Mike',75);
mysql> insert into DemoTable values('Sam',98);使用select语句显示表中的所有记录-
mysql> select *from DemoTable;
这将产生以下输出-
+-------------+--------------+ | StudentName | StudentMarks | +-------------+--------------+ | Chris | 78 | | Robert | 88 | | Mike | 75 | | Sam | 98 | +-------------+--------------+ 4 rows in set (0.00 sec)
这是在以下情况下实现MySQLCASE的查询-
mysql> select *, -> case when StudentMarks > 90 then 'Very Good Score' -> when StudentMarks > 80 then 'Good Score' -> else -> 'Not Good' -> end as Status -> from DemoTable;
这将产生以下输出-
+-------------+--------------+-----------------+ | StudentName | StudentMarks | Status | +-------------+--------------+-----------------+ | Chris | 78 | Not Good | | Robert | 88 | Good Score | | Mike | 75 | Not Good | | Sam | 98 | Very Good Score | +-------------+--------------+-----------------+ 4 rows in set (0.00 sec)