Get MySQL results of parent with both children and children detail counts

Question

So, I have a parent table, that has children records, who at the same time have details (3 level parenting tables). I need to get the parent names, with their respective children and children_detail COUNTs.

parent

• id_parent
• name

children

• id_child
• id_parent
• name

children_detail

• id_detail
• id_child
• description

This works until the second level:

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

How can I also get the third level count in the same SELECT? Thanks!

Answer 1

As your tables are not large, try using a sub-query:

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

Edit

Sorry, the following one should also work:

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

Edit 2

If all else fails, you can use two sub-queries (very bad practice but should be fine for tables of your size):

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