Question

SELECT
(case when tableA.gender = 'Male' then tableB.X) as Male, 
(case when tableA.gender = 'Female' then tableB.X) as Female

...
FROM (MANY TABLES JOINT)
...

GROUP BY tableB.X
ORDER BY count(*) DESC

我正在尝试通过查询另一列（tableB.X）是“男性”还是“女性”来基于一个字段（column_name）返回两列。我该怎么做呢？我仍然需要在DESC中订购这两个列。谢谢。

每行返回一个值和一个性别（2列）。我试图根据性别将值拆分为两列，然后按每个拆分列的计数降序显示..

即。输入表：

value     Gender
-----     ------
AAA       Male
BBB       Female
AAA       Male
CCC       Male
AAA       Female
BBB       Female

即。输出表：

Rank      Male      Female
----      ----      ------
 1        AAA       BBB          (AAA because it has 2 male occurences, BBB has 2 female occurences)
 2        CCC       AAA          (1 occurence each for male and female, ordered descending order)

我也不知道有多少不同的值，所以SQL必须为我做计算。我可以使用两个查询获得结果，使用WHERE gender = male和WHERE gender = female但我想知道我是否可以在一个查询中执行此操作..谢谢！

Answer 1

我认为使用UNION语句可以做到这一点。以下未经过测试：

SELECT
tableB.X as Male,
'' as Female
FROM
...
tableB JOIN tableA
...
WHERE tableA.gender = 'male'

UNION

SELECT
'' as Male,
tableB.X as Female
FROM
...
tableB JOIN tableA
...
WHERE tableA.gender = 'female'

您也可以使用''代替空字符串NULL。

mysql返回基于相同字段的两列

1 个答案: