如何从第二个表中返回具有最后匹配结果的连接表？

Question

表一摘录：

┌─product─────┬────────────sequence─┬─qty─┐
│ A18         │ 1534334750278856541 │   7 │
└─────────────┴─────────────────────┴─────┘

表二摘录：

┌────────────sequence─┬─product─────┬─size─┐
│ 1534331161780089544 │ A18         │    3 │
│ 1534333381672627454 │ A18         │    3 │
│ 1534334750278856540 │ A18         │    3 │
│ 1534334750278856540 │ A18         │    7 │
│ 1534334750278856540 │ A18         │    5 │
└─────────────────────┴─────────────┴──────┘

对于TableOne的每一行，我想在TableTwo中找到具有相同产品名称和TableTwo.sequence <= TableOne.sequence的最后一行

所以给出上面的示例数据，返回结果应该如下：

TableOne.product  = A18
TableOne.qty      = 7
TableOne.sequence = 1534334750278856541 
TableTwo.sequence = 1534334750278856540
TableTwo.size     = 5

谢谢

Answer 1

首先编写一个子查询，在tableTwo中找到符合条件的序列号：

SELECT t1.product, t1.sequence AS t1_sequence, t1.qty, MAX(t2.sequence) AS t2_sequence
FROM tableOne AS t1
JOIN tableTwo AS t2 ON t1.product = t2.t2.product AND t1.SEQUENCE >= t2.sequence
GROUP BY t1.product

然后将其与tableTwo以查找包含该序列的整行。

SELECT product, t1_sequence, t2_sequence, qty, t2_sequence, t2.size
FROM (
    SELECT t1.product, t1.sequence AS t1_sequence, t1.qty, MAX(t2.sequence) AS t2_sequence
    FROM tableOne AS t1
    JOIN tableTwo AS t2 ON t1.product = t2.t2.product AND t1.SEQUENCE >= t2.sequence
    GROUP BY t1.product
) AS joined
JOIN tableTwo AS t2 ON t2.product = joined.product AND t2.sequence = joined.t2_sequence