Having in SQL 服务器的条件过滤器

Question

我正在使用 SQL Server 2016。我正在尝试弄清楚如何使用 having 子句进行条件过滤。

我想给我一个所有 ID、日期和用户名的列表，如果日期在 2018 年之前，则向我显示具有 2-12 个 ID 的用户，如果日期在 2018 年之后，则向我显示具有 2 个 ID 的用户-24 个 ID。我只能考虑合并代码，但这会增加处理时间，有没有其他方法可以更快地完成此操作？

原码：

select [id], [date], [user name]
from [table]
where [date] < '2018-01-01' 
group by [id], [date], [user name]
having count([id]) between 2 and 12) b

联合理念：

select [id], [date], [user name]
from [table]
where [date] < '2018-01-01' 
group by [id], [date], [user name]
having count([id]) between 2 and 12) b

UNION 

select [id], [date], [user name]
from [table]
where [date] >= '2018-01-01' 
group by [id], [date], [user name]
having count([id]) between 2 and 24) b

Answer 1

您可以在 HAVING 语句中使用 OR：

select [id], [date], [user name]
from [table]
group by [id], [date], [user name]
having (
        (count([id]) between 2 and 12 AND [date] < '2018-01-01')
        OR
        (count([id]) between 2 and 24 AND [date] >= '2018-01-01')
       );

仅当您在 HAVING 子句中引用的列是聚合列或包含在 GROUP BY 子句中时才有效

Having in SQL 服务器的条件过滤器

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