存储过程中的SQL条件连接（带/不带参数）

Question

我正在使用SQL Server 2005中的存储过程。如果只有参数不为null，是否可以使用连接？以下是查询示例：

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))

如果INNER JOIN不为空，如何使@username起作用？获得预期结果的最佳方法是什么？

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))

虽然不是最干净的，但却有效。