MySQL的CASE/WHEN流程控制语句

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MySQL中的CASE/WHEN可以进行流程控制判断，比如：

CASE 字段 WHEN 具体值
例如:

id	name	sex	salary
1	A	m	2500
2	B	f	1500
3	C	m	5500
4	D	f	500

运行你所编写的查询语句之后，将会得到以下表:

id	name	sex	salary
1	A	f	2500
2	B	m	1500
3	C	f	5500
4	D	m	500

可以这样：

UPDATE salary SET sex = CASE sex
                        WHEN 'm' THEN 'f'
                        WHEN 'f' THEN 'm'
                        END;

也可以进行范围的判断：
CASE WHEN column BETWEEN … AND …THEN …

mysql> select *,case
    ->          when Salary between 65000 and 100000 then 'high'
    ->          when Salary between 30000 and 65000 then 'low'
    ->          end as 'sal'
    ->          from Employee;
+------+-------+--------+--------------+------+
| Id   | Name  | Salary | DepartmentId | sal  |
+------+-------+--------+--------------+------+
|    1 | Joe   |  70000 |            1 | high |
|    2 | Henry |  80000 |            2 | high |
|    3 | Sam   |  60000 |            2 | low  |
|    4 | Max   |  90000 |            1 | high |
+------+-------+--------+--------------+------+
4 rows in set (0.00 sec)