SQL - 在哪裏使用SELECT別名

Question

我有一段時間讓這個查詢工作。基本上我需要做一個CASE語句來獲取該人的NickName，否則使用他們的FirstName。然後在WHERE語句中，對上面的CASE語句做一個LIKE語句。

我已經能夠得到它的工作，如果我只有做名字/暱稱，但是當我在其他列添加它停止工作。

這裏是我有

SELECT 
    LastName 
    , Company 
    , Status 
    , CASE 
     WHEN NickName = '' THEN FirstName 
     WHEN NickName IS NULL THEN FirstName 
     ELSE NickName 
    END AS FName 
FROM database 
WHERE 
     Status = 'Active' 
    AND Company = '@Company' 
    AND FName + ' ' + LastName LIKE '%@search%' 
    OR LastName + ', ' + FName LIKE '%@search%' 

顯然，上述不工作，因爲我想在我的WHERE子句中使用的別名。我得到

Msg 207, Level 16, State 1, Line 14 
Invalid column name 'FName'. 
Msg 207, Level 16, State 1, Line 15 
Invalid column name 'FName'. 

任何幫助，非常感謝。謝謝！

Answer 1

您可以使用公用表表達式或子查詢來創建FName作爲新結果集的一種虛擬列。你可以使用結果集作爲一種虛擬表，並在where子句中對其進行過濾。

SELECT * 
FROM (
    SELECT 
    LastName 
    , Company 
    , Status 
    , CASE 
     WHEN NickName IS NULL OR NickName = '' THEN FirstName 
     ELSE NickName 
     END AS FName 
    FROM database 
    WHERE Status = 'Active' 
    AND Company = '@Company' 
) FNames 
WHERE FName + ' ' + LastName LIKE '%@search%' 
    OR LastName + ', ' + FName LIKE '%@search%' 

Answer 2

使用CROSS APPLY創建別名

SELECT LastName 
    , Company 
    , Status 
    , FName 
FROM database 
    CROSS APPLY (
     SELECT CASE WHEN NickName = '' THEN FirstName 
        WHEN NickName IS NULL THEN FirstName 
        ELSE NickName 
       END AS FName 
    ) AS CA1 
WHERE Status = 'Active' 
     AND Company = '@Company' 
     AND FName + ' ' + LastName LIKE '%@search%' 
     OR LastName + ', ' + FName LIKE '%@search%' 

Answer 3

你可以不用CASE語句

SELECT * 
FROM (
    SELECT 
     LastName 
     , Company 
     , Status 
     , ISNULL(NULLIF(NickName, ''), FirstName) AS FName 
    FROM database 
    WHERE Status = 'Active' 
     AND Company = '@Company') data 
WHERE (FName + ' ' + LastName LIKE '%' + @search + '%') 
    OR (LastName + ', ' + FName LIKE '%' + @search + '%')