SQL Server语言 - 选择查询中的选择性条件

Question

我有两个表Companies1和Companies2，其中公司名称始终存在于Companies2表中，但可能位于Companies1表中，也可能不在表中。

我需要应用此条件：

CONVERT(VARCHAR(11), GETDATE(), 112) BETWEEN Start AND End

仅当表中存在名称Companies1：

SELECT DISTINCT 
    COALESCE(NULLIF(Company1_Name, ''), Company2_Name) Company
FROM 
    [Companies1] AS C1 
LEFT JOIN 
    [Companies2] AS C2 ON (C1.Company1_Name = C2.Company2_Name) 
WHERE 
    Company1_Name = ('XYZ') 
    AND CONVERT(VARCHAR(11), GETDATE(), 112) BETWEEN Start AND End

我怎样才能做到这一点？

Answer 1

请尝试这样的事情。另外，请不要在 where 子句中的列周围使用函数，因为它会使查询不可优化。

select DISTINCT COALESCE(NULLIF(Company1_Name,''),Company2_Name) Company
FROM [Companies1] as C1 left join [Companies2] AS C2 
on(C1.Company1_Name=C2.Company2_Name) where Company1_Name=('XYZ') 
AND 
CONVERT(VARCHAR(11), getdate(), 112) >= 
        CASE WHEN C1.Company1_Name IS NOT NULL THEN [Start] ELSE CONVERT(VARCHAR(11), getdate(), 112) END
AND 
CONVERT(VARCHAR(11), getdate(), 112) <= 
    CASE WHEN C1.Company1_Name IS NOT NULL THEN [End] ELSE CONVERT(VARCHAR(11), getdate(), 112) END

Answer 2

SELECT DISTINCT COALESCE(NULLIF(Company1_Name,''),Company2_Name) Company
FROM [Companies1] AS C1 LEFT JOIN [Companies2] AS C2 ON (C1.Company1_Name=C2.Company2_Name) WHERE EXISTS Company1_Name=('XYZ') AND 
CONVERT(VARCHAR(11), getdate(), 112) 
IN BETWEEN Start AND End