SQL Server 条件 where 子句

Question

我有以下 where 子句，其开头如下:

DECLARE @Birthdate = 1

SELECT ... 
FROM ... 
JOIN ...
WHERE A.organization_id = 1
  AND LEFT(A.[first_name], 3) = LEFT(B.[first_name], 3)
  AND LEFT(A.[last_name], 3) = LEFT(B.[last_name], 3)

在此之后，我想有条件地执行附加子句。

例如:

• 如果@Birthdate = 1，则添加AND A.[出生日期] = B.[出生日期]
• 否则，请勿添加任何内容

我尝试了以下方法，但似乎都无法正常工作:

示例 1:

 AND (@Birthdate = 1 AND A.[birthdate] = B.[birthdate])

示例 2:

AND ((@Birthdate = 1 AND A.[birthdate] = B.[birthdate]) OR 
     (@Birthdate = 0 AND (A.[birthdate] = B.[birthdate] OR 
                          A.[birthdate] <> B.[birthdate])))

对于我做错了什么有什么建议吗？

Answer 1

您可以使用或来应用过滤器，或者在@Birthdate = 0时返回所有行

SELECT
    ...
FROM
    ...
WHERE
    (
        -- Apply the filter if applicable
        (
            @Birthdate = 1
            and A.[birthdate] = B.[birthdate]
        )
        -- Or return everything
        or @Birthdate <> 1
    )