如果在SQL查詢的WHERE子句

Question

下面是條件我在那裏時，我想對特定用戶

where Completion_Date>= '11/01/2011' 
and Completion_Date<= '12/11/2012' 
and System_user_id = 1234 

及以下數據查詢的WHERE子句是WHERE子句時，我想拉的所有數據用戶：

where Completion_Date>= '11/01/2011' 
and Completion_Date<= '12/11/2012' 

因爲我不想2個獨立的查詢，有沒有辦法添加在where子句，這樣我可以使用單一的查詢，並根據輸入（即SYSTEM_USER_ID），它會決定是否條件在查詢中添加額外的條件。 當我想爲所有用戶的數據&發送一個特定用戶的system_user_id將被髮送時，我將發送-1。

Answer 1

你可以試試下面的方法在這一個變化。

更新查詢

declare @userid int = -1 
if (@userid = -1) 
    BEGIN 

    SELECT * FROM mytable 
    where Completion_Date>= '11/01/2011' 
    and Completion_Date<= '12/11/2012' 
    and userid in 
     (select distinct userID from mytable) 
    end 
ELSE 
    BEGIN 

    SELECT * FROM mytable 
    where Completion_Date>= '11/01/2011' 
    and Completion_Date<= '12/11/2012' 
    and userid = @userid 

end; 

結果：

USERID NAME COMPLETION_DATE 
123  john 2011-11-01 
125  tim  2011-11-02 
127  ron  2011-11-08 

• 參考SQLFIDDLE

要查看特定用戶：

• 參考SQLFIDDLE

---

另一種方法

最新評論後更新從OP

• SQLFIDDLE

查詢：

DECLARE @uid int = -1 
SELECT 
* 
FROM mytable 
WHERE 
(CASE 
    WHEN @uid <> -1 THEN @uid 
    ELSE userid 
    END 
) = userid 

and Completion_Date>= '11/01/2011' 
    and Completion_Date<= '12/11/2012' 
; 

結果：當@uid = -1

USERID NAME COMPLETION_DATE 
123  john 2011-11-01 
125  tim  2011-11-02 
127  ron  2011-11-08 

請評論，如果你已經嘗試了這一點:)

Answer 2

嘗試：

WHERE ((@System_user_id = -1) 
    AND (Completion_Date >= '11/01/2011') 
    AND (Completion_Date <= '12/11/2012')) 
OR ((@System_user_id <> -1) 
    AND (System_user_id = @System_user_id) 
    AND (Completion_Date >= '11/01/2011') 
    AND (Completion_Date <= '12/11/2012')) 

使用公用表表達式（SQL Fiddle）

;WITH CompletionDates AS 
(
    SELECT * 
    FROM MyTable 
    WHERE Completion_Date >= '11/01/2011' 
    AND Completion_Date <= '12/11/2012' 
) 
SELECT * 
FROM CompletionDates 
WHERE (@System_user_id = -1) OR (System_user_id = @System_user_id)