基于当月的动态 SQL 查询

Question

下面是一个 SQL 代码，它从每月数据摘要的联合中创建一个表：

-- Oct 2017

select distinct  a.device_id ,201710 as month_id,
case when group_descr in ('BASE') then 'Basic'
     when group_descr in ('VALUES') then 'Valuable'
     when group_descr in ('PREFERRENCE') then 'Preferr'
     else 'Other'
end as Class
from dbo.DEVICE_HIST a
where a.expired >= '2017-10-01' and a.EFFTV <'2017-10-31'

union

-- Nov 2017
select distinct  a.device_id ,201711 as month_id,
case when group_descr in ('BASE') then 'Basic'
     when group_descr in ('VALUES') then 'Valuable'
     when group_descr in ('PREFERRENCE') then 'Preferr'
     else 'Other'
end as Class
from dbo.DEVICE_HIST a
where a.expired >= '2017-11-01' and a.EFFTV <'2017-11-30'

union

-- Dec 2017
select distinct  a.device_id ,201712 as month_id,
case when group_descr in ('BASE') then 'Basic'
     when group_descr in ('VALUES') then 'Valuable'
     when group_descr in ('PREFERRENCE') then 'Preferr'
     else 'Other'
end as Class
from dbo.DEVICE_HIST a
where a.expired >= '2017-12-01' and a.EFFTV <'2017-12-31'

union

-- Jan 2018
select distinct  a.device_id ,201801 as month_id,
case when group_descr in ('BASE') then 'Basic'
     when group_descr in ('VALUES') then 'Valuable'
     when group_descr in ('PREFERRENCE') then 'Preferr'
     else 'Other'
end as Class
from dbo.DEVICE_HIST a
where a.expired >= '2018-01-01' and a.EFFTV <'2018-01-31'

这是每月运行一次，基于当前月份，我们需要从上个月取 3 个月的数据 - 1，向后。 例如，如果在 2 月运行，则应从 10 月至 12 月运行，如果在 3 月运行，则应从 11 月至 1 月运行。 这将基于当前月份，但有人可以帮我自动化吗？

需要当前月份并返回 - 1 个月，然后再从那里返回 3 个月。 虽然日期计算没有那么复杂，但是如何让查询根据当前月份动态变化呢？

Answer 1

假设这是 SQL SERVER 2005+：

-- Oct 2017
select distinct  a.device_id
                ,CONCAT(CAST(YEAR(a.expired) AS varchar(4)),right('00'+CAST(MONTH(a.expired) AS nvarchar(2)), 2))  as month_id,
                case when group_descr in ('BASE') then 'Basic'
                     when group_descr in ('VALUES') then 'Valuable'
                     when group_descr in ('PREFERRENCE') then 'Preferr'
                     else 'Other'
                end as Class
from @test a
where CONVERT(date, a.expired) >= DATEADD(month, DATEDIFF(month, 0, convert(date, DATEADD(MONTH, -3, GETDATE()))), 0)