SQL你可以把一个if语句放在select过程中吗？

Question

我需要一个if语句添加到我的过程中，这样的事情

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 
) 

正如你可以根据我使用这种或那种方式将lname领域的标志见。 我在if部分收到错误..是不是我在这里不能使用if语句？ 如果不是，我该如何替换if语句？

非常感谢

Answer 1

你可以这样说：

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

只是提供一个备用的答案（因为我觉得一个CASE语句是真正的模拟到SQL IF语句）：

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

试试这个

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