Question

我被告知删除联盟并将查询的上半部分更改为一个，我被告知这很容易，但我无法弄明白。我被告知它会包含类似

的内容

红色（主要颜色）=红色（SilksName）蓝色（主要颜色）=蓝色（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

我认为你没有理由从查询中删除UNION ALL，这是最好的选择，尽管你可以将UNION移动到子查询：

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

如果已要删除UNION，您可以使用此功能：

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

但是我无法想象这种表现比UNION更好。

注意我刚刚看到你的回答，我会选择联接中的CASE而不是OR，case语句会短路，所以当子颜色存在时它不会评估第二部分，而OR将评估两者。

Answer 2

想出来，谢谢

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

从查询中删除联合并将其转换为一个查询？

2 个答案: