從查詢中刪除聯合並將其轉換爲一個查詢？

Question

我被告知刪除工會並將查詢的上半部分改爲一個，我被告知這很容易，但我無法弄清楚。有人告訴我，這將包括像

凡紅（主要顏色）=紅（SilksName） 凡藍（主要顏色）=藍（SilksName） 等

Select S.[Silks_Skey] 
    from [dbo].[Silks] S 
    inner join [dbo].[SubColour] SC on CHARINDEX(SC.[SubColour],S.[SilksName]) <> 0 
    inner join [dbo].[MajorColour] MC on SC.[MajorColour] = MC.[MajorColour] 

    UNION ALL 

    Select S.[Silks_Skey], MC.[MajorColour_Skey] 
    from [dbo].[Silks] S 
    inner join [dbo].[MajorColour] MC on CHARINDEX(MC.[MajorColour],S.[SilksName]) <> 0 

    ORDER BY S.[Silks_Skey] 

Answer 1

想通了謝謝

Select S.[Silks_Skey], MC.[MajorColour_Skey] 
from [dbo].[Silks] S 
left join [dbo].[SubColour] SC on CHARINDEX(SC.[SubColour],S.[SilksName]) <> 0 
inner join [dbo].[MajorColour] MC on SC.[MajorColour] = MC.[MajorColour] 
or CHARINDEX(MC.[MajorColour],S.[SilksName]) <> 0 

Answer 2

我看不出有任何理由爲什麼你應該從查詢中刪除UNION ALL，它是最好的選擇，儘管你可以在UNION移動到一個子查詢：

SELECT S.[Silks_Skey], c.[MajorColour_Skey] 
FROM [dbo].[Silks] S 
     INNER JOIN 
     ( SELECT [Colour] = sc.[SubColour], mc.[MajorColour_Skey] 
      FROM [dbo].[SubColour] sc 
        INNER JOIN [dbo].[MajorColour] mc 
         ON sc.[MajorColour] = mc.[MajorColour] 
      UNION ALL 
      SELECT mc.[MajorColour], mc.[MajorColour_Skey] 
      FROM [dbo].[MajorColour] mc 
     ) c 
      ON CHARINDEX(c.[Colour], S.[SilksName]) <> 0 

如果HAVE刪除UNION，你可以這樣做：

SELECT S.[Silks_Skey], mc.[MajorColour_Skey] 
FROM [dbo].[Silks] S 
     LEFT JOIN [dbo].[SubColour] sc 
      ON CHARINDEX(sc.[SubColour], S.[SilksName]) <> 0 
     INNER JOIN [dbo].[MajorColour] mc 
      ON CASE WHEN sc.SubColour IS NOT NULL AND mc.MajourColour = sc.MajourColour THEN 1 
        ELSE CHARINDEX(mc.[MajorColour], S.[SilksName]) <> 0 
       END <> 0 

但我不能想象這個執行比UNION更好。

注意我的hve剛剛看到你的答案，我會選擇在加入，而不是OR的CASE，case語句會帶有短路，所以當一個subcolour存在，它不評估的第二部分，而OR將評估兩者。