获取具有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级父母表）。我需要获取父名称，以及他们各自的子项和children_detail COUNTs。

父

• id_parent
• 名称

的子

• id_child
• id_parent
• 名称

children_detail

• id_detail
• id_child
• 描述

直到第二级：

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中获得第三级计数？谢谢！

Answer 1

由于您的表格不大，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

修改

抱歉，以下内容也应该有效：

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

如果所有其他方法都失败了，你可以使用两个子查询（非常糟糕的做法，但对于你的大小的表格应该没问题）：

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