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使用WHEN子句实现MySQL CASE语句

2024-05-16 16:20:05 352

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)

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使用WHEN子句实现MySQL CASE语句

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