存儲過程中的SQL條件連接（帶/不帶參數）

Question

我正在使用SQL Server 2005中的存儲過程。如果只有參數不爲空，是否可以使用連接？下面是查詢的一個例子：

ALTER PROCEDURE [dbo].[SPSample] 
@gender varchar(20) = null 
@username varchar(20) = null 
AS 

SELECT 
per.firstName, 
per.lastName, 
per.gender 

FROM person per 
INNER JOIN account ac on ac.idPerson = per.idPerson 

WHERE (
gender = @gender 
AND (@username is null or (@username is not null and @username = acc.username)) 

如何使INNER JOIN只能如果@username不爲空？獲得預期結果的最佳方法是什麼？

Answer 1

ALTER PROCEDURE [dbo].[SPSample] 
@gender varchar(20) = null 
@username varchar(20) = null 
AS 

SELECT 
per.firstName, 
per.lastName, 
per.gender 

FROM person per 
LEFT JOIN account ac 
ON  @username is not null 
    AND @username = ac.username 
    AND ac.idPerson = per.idPerson 

WHERE --(
gender = @gender 
--AND (@username is null or (@username is not null and @username = acc.username)) 

雖然不是最乾淨的，但它的工作原理