如何从最大日期小于表 A 中日期的表 B 中获取值

Question

我有两张桌子；表 A 和表 B。表 A 有 StoreNumber、MatNumber 和 Date。表 B 有 StoreNumber、MatNumber、Date 和 ShipmentValue。我必须从表 B 中获取 StoreNumber 和 MatNumber 的 Shipment 值，因为表 B 中 StoreNumber 和 MatNumber 的最大日期应小于表 A 中相同 StoreNumber 和 MatNumber 的日期（表 A 中的每一行）。请看输出表。

表 A：

StoreNumber MatNumber   Date
  A            9    3/30/2020
  A            9    3/30/2020
  B           10    3/18/2020
  B           10    3/18/2020
  A            9    3/13/2020

表 B：

StoreNumber MatNumber   Date    ShipmentValue
       A           9    3/10/2020   2
       A           9    3/12/2020   3
       A           9    3/18/2020   4
       B          10    3/4/2020    7
       B          10    3/7/2020    9
       B          10    3/16/2020   10

输出：

StoreNumber MatNumber   A.Date  B.Date  ShipmentValue
       A           9    3/30/2020   3/18/2020   4
       A           9    3/30/2020   3/18/2020   4
       B          10    3/18/2020   3/16/2020   10
       B          10    3/18/2020   3/16/2020   10
       A           9    3/13/2020   3/12/2020   3

Answer 1

尝试使用 ROW_NUMBER 并在按 desc 订购日期后选择第一行。

SELECT  A.StoreNumber 
        ,A.MatNumber  
        ,A.Date 
        ,B.Date AS B_Date   
        ,B.ShipmentValue 
FROM    TableA A
LEFT JOIN 
        (
          SELECT  StoreNumber ,MatNumber  , Date   , ShipmentValue
          FROM 
              (
                SELECT ROW_NUMBER() OVER (PARTITION BY StoreNumber, MatNumber ORDER BY DATE DESC ) AS ID,* 
                FROM TableB
              ) A 
          WHERE ID = 1
         ) B
ON   A.StoreNumber  = B.StoreNumber
AND  A.MatNumber    = B.MatNumber

Answer 2

这是一个方便lateral join 的地方：

select a.*, b.date, b.shipmentvalue
from a left join lateral
     (select b.*
      from b
      where b.storenumber = a.storenumber and
            b.matnumber = a.matnumber and
            b.date <= a.date
      order by b.date desc
      fetch first 1 row only
     ) b
     on 1=1;  -- returns rows in a even when there are no matches

编辑：

哇。 Snowflake 实现横向连接，然后以基本方式限制它们。另一种方法更昂贵但应该有效：

select ab.*, b.shipmentValue
from (select a.StoreNumber, a.MatNumber, a.Date, max(b.date) as b_date, b.shipmentvalue
      from a left join
           b 
           on b.storenumber = a.storenumber and
              b.matnumber = a.matnumber and
              b.date <= a.date
      group by a.StoreNumber, a.MatNumber, a.Date
     ) ab join
     b
     on b.storenumber = ab.storenumber and
        b.matnumber = ab.matnumber and
        b.date <= ab.b_date