mysql - 从mysql中的两个表中查找最近的行

Question

我有 2 张桌子

表A

id     user_id    created_date   earning 
1         5        2013-05-05     500
2         4        2013-06-02     900
3         3        2013-03-01     700

表 B

id     user_id    created_date   earning 
1         8        2013-09-05     500
2         4        2013-08-12     200
3         3        2013-02-21     200

具有相同的字段。

我想要的是，为用户找到最新的收入。对于用户 3，我可以找到最新的收入，但对于用户 8，表 A 中没有数据，我找不到最新的收入。

谢谢你

Answer 1

SELECT T.user_id
    , CAST(SUBSTRING_INDEX(GROUP_CONCAT(T.earning ORDER BY T.created_date DESC), ',', 1) AS DECIMAL) AS latest_earning
    FROM (
        SELECT user_id
            , created_date
            , earning
            FROM tableA

        UNION ALL

        SELECT user_id
            , created_date
            , earning
            FROM tableB
    ) T
    GROUP BY T.user_id;

这是SQL Fiddle演示。

Answer 2

试试这个：

select * from (
  select * from (
    select * from tablea
    union
    select * from tableb) x
  order by created_date desc) y
group by user_id

Answer 3

假设用户在特定日期只有 1 次收入，您可以使用以下方法：-

SELECT Sub4.id, Sub4.user_id, Sub4.created_date, Sub4.earning 
FROM (SELECT user_id, MAX(created_date) AS MaxCreatedDate
FROM (SELECT user_id, created_date
FROM tableA
UNION ALL
SELECT user_id, created_date
FROM tableB) Sub1) Sub2
INNER JOIN (SELECT user_id, created_date, earning
FROM tableA
UNION ALL
SELECT user_id, created_date, earning
FROM tableB) Sub4
ON Sub2.user_id = Sub4.user_id
AND Sub2.MaxCreatedDate = Sub4.created_date