mysql - 获取包含子项和子项详细信息计数的父项的 MySQL 结果

Question

所以，我有一个父表，它有子记录，同时有详细信息(3 级父表)。我需要获取 parent 姓名，以及他们各自的 child 和 children_detail COUNT。

parent

• id_parent
• 姓名

child

• id_child
• id_parent
• 姓名

children_detail

• id_detail
• id_child
• 描述

这一直有效到第二层:

SELECT parent.id_parent, parent.name,
COUNT(pos.id_pos) AS q
FROM parent
LEFT JOIN children ON children.id_parent = parent.id_parent
GROUP BY parent.id_parent ORDER BY parent.name

如何在同一个 SELECT 中也获得第三级计数？谢谢!

Answer 1

由于您的表不大，请尝试使用子查询:

SELECT parent.id_parent, parent.name,
COUNT(pos.id_pos) AS q,
(SELECT COUNT(*) FROM children_detail cd WHERE cd.id_child = children.id_child) as cdc
FROM parent
LEFT JOIN children ON children.id_parent = parent.id_parent
GROUP BY parent.id_parent ORDER BY parent.name

编辑

抱歉，下面的应该也可以:

SELECT parent.id_parent, parent.name,
  COUNT(pos.id_pos) AS q,
  COUNT(cdc.id_detail) as cdc
FROM parent
  LEFT JOIN children ON children.id_parent = parent.id_parent
  LEFT JOIN children_detail cdc on cdc.id_child = children.id_child
GROUP BY parent.id_parent, parent.name
ORDER BY parent.name

编辑2

如果一切都失败了，您可以使用两个子查询(非常糟糕的做法，但对于您的大小的表来说应该没问题):

SELECT parent.id_parent, parent.name,
  COUNT(pos.id_pos) AS q,
  (SELECT COUNT(*) FROM children_detail cd WHERE cd.id_child IN (SELECT cc.id_child FROM children cc where cc.id_parent = c.id_parent)) as cdc
FROM parent
  LEFT JOIN children c ON c.id_parent = parent.id_parent
GROUP BY parent.id_parent 
ORDER BY parent.name