MySQL选择在一列上具有公共值但在另一列上具有公共值的行

Question

这是my table in SQL Fiddle。我想为每个children_id找到1行，其中存在最大in_time。所以预期的输出是：

----+------------+
id  |  in_time   |
----+------------+
16  | 1518909618 |
18  | 1518913186 |
17  | 1518909862 |
----+------------+

这是我的查询，但未提供预期数据：

SELECT a.id, a.in_time
FROM `ca_attendance` AS a
LEFT JOIN (
    SELECT MAX(id) AS id, in_time
    FROM ca_attendance
    GROUP BY children_id
) AS b ON a.id = b.id AND a.in_time = b.in_time

Answer 1

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