SQL你可以把一個if語句放在select過程中嗎？

Question

我需要一個if語句添加到我的過程中，這樣的事情

CREATE PROCEDURE [dbo].[myProcedure] 
    @name VARCHAR(8000) = NULL 
,@lname VARCHAR(8000) = NULL 
,@flag CHAR(1) = NULL 


AS 
BEGIN 
SET NOCOUNT ON; 
    WITH t 
    (name 
    ,lname 
    ) 

AS 
(
    SELECT DISTINCT 
    * FROM mytable 
    WHERE 
    (@name IS NULL OR @name = name) 
    IF @flag = 'c' 
    BEGIN 
     AND (@lname IS NULL OR @lname = 'Doe') 
    END 
    ELSE 
    BEGIN 
    AND (@lname IS NULL OR @lname = lname) 
    END 
) 

正如你可以根據我使用這種或那種方式將lname領域的標誌見。 我在if部分收到錯誤..是不是我在這裏不能使用if語句？ 如果不是，我該如何替換if語句？

非常感謝

Answer 1

你可以這樣說：

SELECT DISTINCT * 
FROM mytable 
WHERE 
    (@name IS NULL OR @name = name) 
    AND 
    (
     (@flag = 'c' AND (@lname IS NULL OR @lname = 'Doe')) 
     OR 
     (@flag != 'c' AND (@lname IS NULL OR @lname = lname)) 
    ) 

Answer 2

只是提供一個備用的答案（因爲我覺得一個CASE語句是真正的模擬到SQL IF語句）：

SELECT 
DISTINCT 
    * 
FROM 
    mytable 
WHERE 
    (@name IS NULL OR @name = name) 
    AND 
    (@lname is NULL OR @lname = 
    CASE 
     WHEN @flag ='c' THEN 'Doe' 
     ELSE lname 
    END 
    ) 

Answer 3

試試這個

.... 
WHERE 
(@name IS NULL OR @name = name) AND 
(
    (@flag = 'c' AND (@lname IS NULL OR @lname = 'Doe')) OR 
    (@lname IS NULL OR @lname = lname) 
)