JOIN中的SQL查詢優化問題

Question

我在一個查詢中有多個JOIN語句，我必須檢查JOIN中的兩個設置。如何以最好的方式做到這一點？

table: WebSettings 
------------------------------------------------------- 
Name   | Setting | InstID | WebSettingID 
------------------------------------------------------- 
'EnableError' | 2 | 1111 | 1 
'ErrorsSetting' | 0 | 2121 | 2 

Index : 

InstID 
WebSettingID (InstID) 


table: InstProd 
------------------------------------------------------- 
InstitutionID | Name 
------------------------------------------------------- 
1111  | 'Bank of Ind' 
2121  | 'IOB' 


Index : 

InstitutionID 


SELECT 

Column1, 
DATEADD(.....) 

FROM 
dbo.InstProd I 
INNER JOIN dbo.WebSettings WS1 ON 
WS1.InstitutionID = I.InstID AND 
WS1.Name = 'EnableError' AND WS1.Setting=2 
INNER JOIN dbo.WebSettings WS2 ON 
WS2.InstitutionID = I.InstID AND 
WS2.Name = 'ErrorsSetting' AND WS2.Setting=0 
WHERE..... 

我要檢查在JOIN

一個WebSettings = 2和other = 0是否有這樣做的一個最好的解決辦法？

Answer 1

是的，你不需要加入WebSettings兩次，雖然你沒有發表您預期的輸出，所以我不知道到底該怎麼做，而是調整這個：

SELECT <column1>,<column2>, 
     MAX(CASE WHEN ws.Name = 'EnableError' AND ws.settings = 2 THEN <YourDesiredColumn> END) as enable_column, 
     MAX(CASE WHEN ws.Name = 'ErrorsSetting' AND ws.settings = 0 THEN <YourDesiredColumn2> END) as Errors_column 
FROM bo.InstProd I 
INNER JOIN dbo.WebSettings WS1 ON 
WS1.InstitutionID = I.InstID AND 
(WS.Name,ws.setting) in (('EnableError',2),('ErrorsSetting',0)) 
GROUP BY <column1>,<column2> 

這將就像查詢一樣，在同一行中爲您提供啓用和錯誤列。

Answer 2

最小化JOINS可能會導致你期待什麼，如果你不使用WS2

SELECT 
Column1, 
DATEADD(.....) 

FROM 
dbo.InstProd I 
INNER JOIN dbo.WebSettings WS1 ON WS1.InstitutionID = I.InstID 
           AND (WS1.Name = 'EnableError' 
            AND WS1.Setting = 2) 
           OR (WS1.Name = 'ErrorsSetting' 
            AND WS1.Setting = 0) 
WHERE..... 

Answer 3

您可以決定不使用JOIN，因爲我下面的方法解決

如果希望所有InstProd與EnableError = 2和ErrorSettings = 0

試試這個：

SELECT I.* 
FROM InstProd I 
WHERE EXISTS 
    (SELECT 'EnableError = 2' 
     FROM WebSettings WS 
     WHERE WS.InstID = I.InstitutionID 
     AND WS.Name = 'EnableError' AND WS.Setting = 2) 
AND EXISTS 
    (SELECT 'EnableError = 2' 
     FROM WebSettings WS 
     WHERE WS.InstID = I.InstitutionID 
     AND WS.Name = 'ErrorSettings' AND WS.Setting = 0) 

如果希望所有InstProd與檢查約兩設定值

試試這個：

SELECT I.*, 
CASE 
    WHEN 
     (SELECT COUNT(1) 
     FROM WebSettings WS 
     WHERE WS.InstID = I.InstitutionID 
     AND WS.Name = 'EnableError' AND WS.Setting = 2) > 0 
     AND 
     (SELECT COUNT(1) 
     FROM WebSettings WS 
     WHERE WS.InstID = I.InstitutionID 
     AND WS.Name = 'ErrorSettings' AND WS.Setting = 0) > 0 
    THEN 'OK' 
    ELSE 'KO' 
END 
FROM InstProd I