Question

我需要显示父表中来自sql的记录，这些记录的子记录少于4（根本没有子记录也可以），需要SQL查询。

Answer 1

以下是查询：

SELECT
  pt.id, pt.somefield, COUNT(pt.id) as c
FROM
  parenttable pt
LEFT OUTER JOIN
  chiledtable ct
ON
  ct.parenttable_id = pt.id
GROUP BY
  pt.id
HAVING
  c <= 4

Answer 2

您可以使用子查询来计算子行数：

select  *
from    ParentTable as p
left join
        (
        select  parentid
        ,       count(*) as cnt
        from    ChildTable
        group by
                parentid
        ) as c
on      c.parentid = p.id
where   c.cnt <= 3

显示父表中具有小于4的子记录的记录

2 个答案: