TSQL：NULL的「IN」的條款

Question

我有一個需要篩選記錄其中：

NotificationRead = 0 || NULL --> IF GetRead = 0 
NotificationRead = 1 --> IF GetRead = 1 
NotificationRead = 0 || 1 || NULL --> IF GetRead = NULL 

這裏是我使用這個查詢：

DECLARE @GetRead BIT 
DECLARE @Query VARCHAR(20) 

SET @GetRead = NULL 

IF @GetRead = 0 SET @Query = '0,NULL' 
ELSE IF @GetRead = 1 SET @Query = '1' 
ELSE SET @Query = '0,1,NULL' 

SELECT * FROM vwNotifications WHERE NotificationRead IN (@Query) 

上面的查詢基本上失敗當我在IN條款中提供NULL時。 我知道爲什麼感謝this question。

但是，如果我採取的方法爲這個問題的答案建議（使用NotificationRead IN (@Query) OR NotificationRead IS NULL），我得到那裏NotificationRead = NULL時，我不需要他們，例如所有記錄，當@GetRead = 1

能否請您指出我的正確的方向嗎？

Answer 1

不，問題在於您提供的值是字符串。

1 IN (1, 2) -- true. 
1 IN ('1, 2') -- false. 

試試這個：

SELECT * 
FROM vwNotifications 
WHERE (@GetRead = 0 AND (NotificationRead = 0 OR NotificationRead IS NULL)) 
OR (@GetRead = 1 AND NotificationRead = 1) 
OR (@GetRead IS NULL AND (NotificationRead IN (0, 1) OR 
          NotificationRead IS NULL)) 

Answer 2

其他人可能有更好的辦法，但我會移動你的選擇到每個「如果」語句，並相應修改。

IF @GetRead = 0 
    SELECT * FROM vwNotifications WHERE NotificationRead IS NULL or NotificationRead = 0 
ELSE IF @GetRead = 1 
    SELECT * FROM vwNotifications WHERE NotificationRead = 1 
ELSE 
    SELECT * FROM vwNotifications WHERE NotificationRead IS NULL or NotificationRead in 0, 1 

注意：請不要在生產代碼中使用SELECT *。爲您的列命名。

Answer 3

幾個選項：

DECLARE @T TABLE (ID INT IDENTITY(1,1), Notify INT) 
DECLARE @GetRead BIT 
SET @GetRead = 0 

INSERT INTO @T 
     (Notify) 
VALUES (0 -- Notify - int 
     ) 

INSERT INTO @T 
     (Notify) 
VALUES (1 -- Notify - int 
     ) 

INSERT INTO @T 
     (Notify) 
VALUES (NULL -- Notify - int 
     ) 

SELECT * 
FROM @t t 
WHERE @GetRead IS NULL 
    OR (@GetRead = 0 AND (t.Notify =0 OR t.Notify IS NULL)) 
    OR (@getRead = 1 AND t.Notify = @GetRead) 

SELECT * 
FROM @t t 
WHERE @GetRead IS NULL 
    OR ISNULL(t.notify, 0) = @GetRead