return 仅在多个重复 parent 的孩子 table 上最后插入 parent id

Question

我正在尝试获取孩子 table 上最后插入的 parents id 的值，然后加入 grandparents table 得到属性和它们的总数。

这是我的 table 结构：

parents
+------------
|pid | item |
+----+------+
| 1  | ite1 |
| 2  | ite2 |
+-----------+

childs
+-------------+
| cid  | pid  |
+------+------+
| 1    | 1    | -- not
| 2    | 1    | ---- row to be selected(last inserted to join grandparents)
| 3    | 2    | -- not 
| 4    | 2    | ---- row to be selected(last inserted to join grandparents)
+-------------+

grandparents
+----------------------+
| gid | cid | property |
+-----+-----+----------+
| 1   | 1   | 1200     |
| 2   | 1   | 1500     |
| 3   | 2   | 101      |
| 4   | 2   | 303      |
| 5   | 3   | 600      |
| 6   | 3   | 10       |
| 7   | 4   | 335      |
| 8   | 4   | 250      |
+----------------------+

结果

+----------------------------+
| item   | cid  |  property  |
+--------+------+------------+
| ite1   | 2    | 101        |
| ite1   | 2    | 303        |
| ite1   | 4    | 335        |
| ite1   | 4    | 250        |
+----------------------------+

Total property results : sum(101 + 303 +335 + 250) =   989

我试过这个查询，但 return/ 包括导致的行（与孩子上显示的不同）总grandparentstable

query:

SELECT g.property from grandparents g
join childs c on g.cid = c.cid
join parents p on c.pid = p.pid
where c.pid in (select DISTINCT pid from childs) and c.pid = 1

Answer 1

您可以尝试使用子查询来获取 MAX(cid) 然后通过子查询的 cid

执行 JOIN

SELECT g.property 
from grandparents g
join (
    SELECT pid ,MAX(cid) cid
    FROM childs 
    GROUP BY pid  
) c on g.cid = c.cid
join parents p on c.pid = p.pid

return 仅在多个重复 parent 的孩子 table 上最后插入 parent id

return only last inserted parent id on childs table of multiple duplicate parents ids

mysql

sql

greatest-n-per-group