SQL选择union中的多个项目

Question

我正在执行几个选择并希望计算重叠.例:

SELECT id FROM foo WHERE ...
SELECT id FROM bar WHERE ...
SELECT id FROM baz WHERE ...

分别调用这些查询a,b和c.假设给出(1,2,3,4,5),b给出(1,3,5),c给出(4,5,6).我想结合这些并计算多重性.对于上面的例子,我正在寻找的结果是

id | multiplicity
-----------------
1  | 2
2  | 1
3  | 2
4  | 2
5  | 3
6  | 1

如何在一个查询中在MySQL5中执行此操作？(a,b和c部分可以是普通选择或存储过程).

Answer 1

我目前无法验证这一点,但我相信这会奏效

SELECT id, count(id) AS multiplicity 
FROM
(
    SELECT id FROM foo WHERE ...
    UNION ALL
    SELECT id FROM bar WHERE ...
    UNION ALL
    SELECT id FROM baz WHERE ...
) AS TablesTogether
GROUP BY id