获取从一对多关系火鸟加入的最后一条记录

Question

我目前正在研究一个 Firebird 数据库，其中产品到产品成本表是一对多的。 我需要在产品列表脚本中包含最新的成本（最高 ID）。

我不确定如何在一对多的关系上做到这一点。

select SPLU.SHOPPRODUCTSPLUID,SPLU.plu, SPLU.description, SPLU.SHOPPRODUCTSID,
       SG.GROUPNAME, SCOST.NORMALCOST, splu.sellprice1, SSL.NAME as fmSuppliername,
       sdl.NAME as fmDeptName,SS.MAINSUPPLIER as fmMainSupplier, SS.UNITSPERCARTON as UPC
from SHOPPRODUCTSPLU SPLU
join SHOPPRODUCTS SP
    on SP.SHOPPRODUCTSID = SPLU.SHOPPRODUCTSID 
join SHOPGROUPLOOKUP SG
    on SG.SHOPGROUPLOOKUPID = SP.SHOPGROUPLOOKUPID and SP.STOREID = SG.STOREID 
join SHOPSUPPLIER SS
    on SS.SHOPPRODUCTSID = SP.SHOPPRODUCTSID and SS.STOREID = SP.STOREID
JOIN SHOPSUPPLIERLOOKUP SSL
    ON SSL.SHOPSUPPLIERLOOKUPID = SS.SHOPSUPPLIERLOOKUPID
join SHOPDEPTLOOKUP SDL
    ON SDL.SHOPDEPTLOOKUPID = SG.SHOPDEPTLOOKUPID
join SHOPPRODUCTSCOSTHST SCOST
    on SCOST.SHOPPRODUCTSID = SPLU.SHOPPRODUCTSID 
where SP.STOREID = 1 and SPLU.ACTIVEITEM = 'TRUE' and SP.ACTIVEITEM = 'TRUE'

当我们只需要最新的时，我加入SHOPPRODUCTCOSTHST现在将在下表中记录每项费用。

当前 output

Answer 1

一种解决方案是在SHOPPRODUCTSCOSTHST上的联接中添加一个条件，以过滤具有最高 id 的匹配记录：

join SHOPPRODUCTSCOSTHST SCOST
    on SCOST.SHOPPRODUCTSID = SPLU.SHOPPRODUCTSID 
    and SCOST.SHOPPRODUCTSCOSTHSID = (
        select max(SCOST1.SHOPPRODUCTSCOSTHSID)
        from SHOPPRODUCTSCOSTHST SCOST1
        where SCOST1.SHOPPRODUCTSID = SPLU.SHOPPRODUCTSID
    )

如果SHOPPRODUCTSCOSTHSID是表SHOPPRODUCTSCOSTHST中的唯一键，则可以稍微简化一下：

join SHOPPRODUCTSCOSTHST SCOST
    on SCOST.SHOPPRODUCTSCOSTHSID = (
        select max(SCOST1.SHOPPRODUCTSCOSTHSID)
        from SHOPPRODUCTSCOSTHST SCOST1
        where SCOST1.SHOPPRODUCTSID = SPLU.SHOPPRODUCTSID
    )

对于此处的性能，您需要SCOST(SHOPPRODUCTSID, SHOPPRODUCTSCOSTHSID)上的索引。

Answer 2

一种可能的解决方案是使用 CTE。

您不想使用我建议的方法的一些因素是您的 SHOPPRODUCTCOSTHST 表是否有大量行。 另一个因素是该查询是否非常频繁地执行。

CTE 将用于获取按 SHOPPRODUCTSID 分组的 SHOPPRODUCTCOSTHST 的 MAX ID。 然后，我将在主查询中使用该 CTE，并将您的 INNER JOIN SCOST 限制在 CTE.MAX_SHOPPRODUCTSCOSTHSTID = SCOST.SHOPPRODUCTCOSTHSTID 上。 每个 SHOPPRODUCTSID 只会返回一行。

下面是一个例子。

  WITH MAXCOSTHST
    AS (
        SELECT SHOPPRODUCTSID
            ,MAX(SHOPPRODUCTSCOSTHSTID) MAX_SHOPPRODUCTSCOSTHSTID
        FROM SHOPPRODUCTSCOSTHST
        GROUP BY SHOPPRODUCTSID
        )
    SELECT SPLU.SHOPPRODUCTSPLUID
        ,SPLU.plu
        ,SPLU.description
        ,SPLU.SHOPPRODUCTSID
        ,SG.GROUPNAME
        ,SCOST.NORMALCOST
        ,splu.sellprice1
        ,SSL.NAME AS fmSuppliername
        ,sdl.NAME AS fmDeptName
        ,SS.MAINSUPPLIER AS fmMainSupplier
        ,SS.UNITSPERCARTON AS UPC
    FROM SHOPPRODUCTSPLU SPLU
    JOIN SHOPPRODUCTS SP ON SP.SHOPPRODUCTSID = SPLU.SHOPPRODUCTSID
    JOIN SHOPGROUPLOOKUP SG ON SG.SHOPGROUPLOOKUPID = SP.SHOPGROUPLOOKUPID
        AND SP.STOREID = SG.STOREID
    JOIN SHOPSUPPLIER SS ON SS.SHOPPRODUCTSID = SP.SHOPPRODUCTSID
        AND SS.STOREID = SP.STOREID
    JOIN SHOPSUPPLIERLOOKUP SSL ON SSL.SHOPSUPPLIERLOOKUPID = SS.SHOPSUPPLIERLOOKUPID
    JOIN SHOPDEPTLOOKUP SDL ON SDL.SHOPDEPTLOOKUPID = SG.SHOPDEPTLOOKUPID
    JOIN MAXCOSTHST ON MAXCOSTHST.SHOPPRODUCTSID = SPLU.SHOPPRODUCTSID
    JOIN SHOPPRODUCTSCOSTHST SCOST ON SCOST.SHOPPRODUCTSID = SPLU.SHOPPRODUCTSID
        AND MAXCOSTHST.MAX_SHOPPRODUCTSCOSTHSTID = SCOST.SHOPPRODUCTSCOSTHSTID
    WHERE SP.STOREID = 1
        AND SPLU.ACTIVEITEM = 'TRUE'
        AND SP.ACTIVEITEM = 'TRUE'