寫這個查詢的更好的方法

Question

我想知道如果我可以替換下面的連接，並減少ISNULL包裹整個選擇的需要？

SELECT ISNULL(
(
SELECT Locale FROM Users WHERE UserGuid = @UserGuid), 
(SELECT Locale FROM Companies WHERE CompanyGuid = 
    (SELECT CompanyGuid FROM UserCompany WHERE UserGuid = @UserGuid) 
)) 

Answer 1

我認爲這將是等效的：

SELECT ISNULL(u.Locale, c.Locale) 
FROM Companies c 
INNER JOIN UserCompany uc ON c.CompanyGuid = uc.CompanyGuid 
LEFT OUTER JOIN Users u ON uc.UserGuid = u.UserGuid 
WHERE uc.UserGuid = @UserGuid 

注：此假設UserGuid是在用戶和UserCompany獨特。