现在有一个表,字段age和type,type = 1的时候需要age降序排列,type = 2的时候age升序排列。一开始觉得很简单啊,于是就写:
SELECT * FROM table_a ORDER BY CASE WHEN type = 1 THEN 'age DESC' WHEN type = 2 THEN 'age ASC' END
后来发现,根本不行!于是又换方法
SELECT * FROM table_a ORDER BY IF(type = 1,'age DESC','age ASC')
然鹅又失败了。于是在朋友提点下,最终解决办法:
方法一:使用union all
SELECT * FROM table_a WHERE type = 1 ORDER BY age DESC
UNION ALL
SELECT * FROM table_a WHERE type = 2 ORDER BY age ASC
方法二:当type = 2的时候把age字段变成负数,然后全部降序排序
SELECT type
,(CASE WHEN type = 1 THEN age * 1 WHEN type = 2 THEN age * -1 END) field
FROM table_a
ORDER BY field DESC