如何连接依赖于外部组的计数

Question

我有一张看起来像这样的表：

id | mid | oid
 1 | 400 | 1
 2 | 400 | NULL
 3 | 401 | 1
 4 | 403 | NULL

我正在尝试返回MID，null OID的记录数和NOT null oid的记录数

目前我正在使用它：

SELECT 
(SELECT COUNT(id) FROM drp_ledger WHERE oid IS NULL) AS que,
(SELECT COUNT(id) FROM drp_ledger WHERE oid IS NOT NULL) AS finished, 
`mid` FROM drp_ledger GROUP BY `mid`

然而，这会返回NULL和NOT NULL oid的整数。

所以我接着尝试使用JOIN我觉得我很接近，但我不能让它发挥作用。

SELECT l.`mid`, que, finished FROM drp_ledger AS l
JOIN (SELECT COUNT(id) AS que FROM drp_ledger WHERE oid IS NULL GROUP BY `mid`) AS q ON q.`mid` =  l.`mid`
JOIN (SELECT COUNT(id) AS finished FROM drp_ledger WHERE oid IS NOT NULL GROUP BY `mid`) AS f ON f.`mid` = l.`mid`

我想回复：

mid | que | finished
400 |  1  |   1
401 |  0  |   1
403 |  1  |   0

Answer 1

无需加入！

SELECT
  mid,
  SUM(IF(oid IS NULL,1,0)) AS oid_null,
  SUM(IF(oid IS NOT NULL,1,0)) AS oid_not_null
FROM tablename
GROUP BY mid

Answer 2

您已关闭，但忘记在子查询中选择mid。