將IN替換爲EXISTS或COUNT。怎麼做。這裏缺少什麼？

Question

我在查詢中使用了IN關鍵字。由於我使用嵌套查詢，並且想要替換In和Exists，這是由於我的老人告訴我可能會出現的性能問題。

我錯過了一些專欄，你在這個查詢中查找什麼。該查詢包含一些用於可讀性的別名。

我該如何刪除它。

SELECT TX.PK_MAP_ID AS MAP_ID 
     , MG.PK_GUEST_ID AS Guest_Id 
     , MG.FIRST_NAME 
     , H.PK_CATEGORY_ID AS Preference_Id 
     , H.DESCRIPTION AS Preference_Name 
     , H.FK_CATEGORY_ID AS Parent_Id 
     , H.IMMEDIATE_PARENT AS Parent_Name 
     , H.Department_ID 
     , H.Department_Name 
     , H.ID_PATH, H.DESC_PATH 
FROM   
    dbo.M_GUEST AS MG 
     LEFT OUTER JOIN 
    dbo.TX_MAP_GUEST_PREFERENCE AS TX 
      ON 
       (MG.PK_GUEST_ID = TX.FK_GUEST_ID) 
     LEFT OUTER JOIN 
    dbo.GetHierarchy_Table AS H 
      ON 
       (TX.FK_CATEGORY_ID = H.PK_CATEGORY_ID) 
WHERE  
    (MG.IS_ACTIVE = 1) 
     AND 
    (TX.IS_ACTIVE = 1) 
     AND 
    (H.Department_ID IN -----How to remove this IN operator with EXISTS or Count() 
       ( 
       SELECT C.PK_CATEGORY_ID AS DepartmentId 
       FROM 
        dbo.TX_MAP_DEPARTMENT_OPERATOR AS D 
         INNER JOIN 
        dbo.M_OPERATOR AS M 
          ON 
           (D.FK_OPERATOR_ID = M.PK_OPERATOR_ID) 
            AND 
           (D.IS_ACTIVE = M.IS_ACTIVE) 
         INNER JOIN 
        dbo.L_USER_ROLE AS R 
          ON 
           (M.FK_ROLE_ID = R.PK_ROLE_ID) 
            AND 
           (M.IS_ACTIVE = R.IS_ACTIVE) 
         INNER JOIN 
        dbo.L_CATEGORY_TYPE AS C 
          ON 
           (D.FK_DEPARTMENT_ID = C.PK_CATEGORY_ID) 
            AND 
           (D.IS_ACTIVE = C.IS_ACTIVE) 
       WHERE  
        (D.IS_ACTIVE = 1) 
         AND 
        (M.IS_ACTIVE = 1) 
         AND 
        (R.IS_ACTIVE = 1) 
         AND 
        (C.IS_ACTIVE = 1) 
      )--END INNER QUERY 
    )--END Condition 

如果我用EXISTS或COUNT取代IN，可能會出現什麼新問題？

Answer 1

基本上，我明白你的問題，你問我怎麼能代替這個：

where H.department_id in (select departmentid from...) 

與此：

where exists (select...) 

或本：

where (select count(*) from ...) > 1 

這是非常坦率的。一種方法可能是這樣的：

WHERE... 
    AND EXISTS (select c.pk_category_id 
       from tx_map_department_operator d 
       inner join m_operator as m 
        on d.fk_operator_id = m.pk_operator_id 
       inner join l_user_role l 
        on m.fk_role_id = r.pk_role_id 
       inner join l_category_type c 
        on d.fk_department_id = c.pk_category_id 
       where h.department_id = c.pk_category_id 
       and d.is_active = 1 
       and m.is_active = 1 
       and r.is_active = 1 
       and c.is_active = 1 
      ) 

我刪除了is_active上的額外連接，因爲它們是多餘的。您應該測試它如何與索引一起運行，因爲這可能會更快。但我對此表示懷疑。但它是值得的比較無論是更快地添加加盟條款（join on ... and x.is_active=y.is_active），或在where子句（x.is_active=1 and y.is_active=1 and z.is_active=1...）

在檢查和我建議你只是用exists，而不是count(*)，因爲我知道，存在應該在找到1行後停止，而計數可能會繼續執行直到完成，然後與您的參考值（count> 1）進行比較。

另外，這是一個奇怪的列命名標準，你有。你真的有主鍵的PK前綴和外鍵的FK前綴嗎？我從來沒有見過。