SQL WHERE在多對多或多對多的空

有誰知道一種方法來簡化這個WHERE表達式？SQL WHERE在多對多或多對多的空

WHERE  (
        (@UserSpecialtyID in 
         (
          SELECT  CharacteristicSpecialties_Id 
          FROM  ModalityVariantSpecialty 
          WHERE  ModalityVariants_Id = ModalityVariants.Id 
         ) 
        ) 
        OR 
        NOT EXISTS 
         (
          SELECT  CharacteristicSpecialties_Id 
          FROM  ModalityVariantSpecialty 
          WHERE  ModalityVariants_Id = ModalityVariants.Id 
         ) 
       )

來源

2011-03-14 CodeGrue

你能發表整個聲明嗎？ – steinar 2011-03-14 21:21:41

WHERE (
     @UserSpecialtyID in 
     (
      SELECT  COALESCE(CharacteristicSpecialties_Id, A.A) 
      FROM  (SELECT @UserSpecialtyID A) A LEFT JOIN ModalityVariantSpecialty 
      ON   ModalityVariants_Id = ModalityVariants.Id 
     ) 
    )

這個效果很好，如果CharacteristicSpecialties_Id是一個非NULLABLE場。

來源

2011-03-14 21:23:39 RichardTheKiwi

COALESCE的開銷是多少？ – CodeGrue 2011-03-16 13:01:32

@CodeGrue在這種情況下幾乎可以忽略不計 – RichardTheKiwi 2011-03-16 19:04:25

像這樣的東西應該可能工作，但我不完全清楚你的表的關係。如果你能解釋關係，我可以舉一個更好的例子。

SELECT 
    * 
FROM MadalityVariants mv 
LEFT JOIN ModalityVariantSpecialty mvs on mvs.ModalityVariants_ID = mv.ID 
WHERE 
    @UserSpecialtyID = mvs.CharacteristicSpecialties_ID 
    OR 
    mvs.CharacteristicSpecialties_ID is null

來源

2011-03-14 21:23:17

這裏是我的嘗試：

WHERE @UserSpecialtyID = COALESCE 
     (
     SELECT TOP 1 CharacteristicSpecialties_Id 
     FROM ModalityVariantSpecialty 
     WHERE ModalityVariants_Id = ModalityVariants.Id 
     ORDER BY 
       CASE WHEN CharacteristicSpecialties_Id = UserSpecialtyID THEN 1 
        ELSE 2 END ASC 
     ), @UserSpecialtyID)

如果ModalityVariants_Id和UserSpecialtyID同時匹配，子查詢返回CharacteristicSpecialties_Id和where成功
如果只是ModalityVariants_Id匹配，子查詢返回不同的ID ，並且where失敗
如果兩者都不匹配，則子查詢返回NULL，C OALESCE返回@UserSpecialtyID和where成功

也許最明顯的是各種約翰Hartsock的回答，與子查詢，以確保left join不添加任何行。

select * 
from ModalityVariants mv 
left join 
     (
     select distinct ModalityVariants_ID 
     ,  CharacteristicSpecialties_ID 
     from ModalityVariantSpecialty 
     ) as mvs 
on  mvs.ModalityVariants_ID = mv.ID 
where @UserSpecialtyID = mvs.CharacteristicSpecialties_ID 
     OR 
     mvs.CharacteristicSpecialties_ID is null

我會投票給約翰的回答:)

來源

2011-03-14 21:23:29 Andomar

爲什麼會增加併發症？在我看來，Coalesce和SubQuery實際上會讓這個運行變慢。不會左連接更容易？ – 2011-03-14 21:28:38

@John Hartsock：好吧，左連接可能會添加額外的行，如果多行包含匹配的'CharacteristicsSpecialties_ID' – Andomar 2011-03-14 21:33:14

我假定這是一個在桌子上ModalityVariants

將這項工作（該SQL未經測試）一個SELECT的WHERE子句？

SELECT * 
FROM ModalityVariants 
LEFT OUTER JOIN ModalityVariantSpeciality 
       ON ModalityVariants.Id = ModalityVariants_ID 
WHERE CharacteristicSpecialities_Id = @UserSpecialityID or  
     CharacteristicSpecialities_Id is NULL

來源

2011-03-14 21:26:27

SQL WHERE在多對多或多對多的空

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