Question

我有一个项目表：

create table #items (
        ItemId int identity(1,1) primary key,
        GroupId int null,
        CreatedTimestamp datetime)

insert into #items values   (1, '2015-01-01'),
                            (2, '2015-02-02'),
                            (3, '2015-03-03'),
                            (1, '2015-06-01'),
                            (2, '2015-09-02'),
                            (2, '2015-10-02'),
                            (1, '2016-05-05'),
                            (1, '2016-07-16'),
                            (2, '2016-03-01')

我想检索具有规则的项目，即每12个月内每个GroupId可能只有一行（从每个GroupId的最小CreatedTimestamp开始）。

因此，对于上面的数据集，将返回行1,2,3,6和8：

ItemId GroupId CreatedTimestamp
------ ------- -----------
1      1       2015-01-01  - yes (1st in group 1)
2      2       2015-02-02  - yes (1st in group 2)
3      3       2015-03-03  - yes (1st in group 3)
4      1       2015-06-01  - no  (within 12 months of item in group 1)
5      2       2015-09-02  - no  (within 12 months of item in group 2)
6      2       2015-10-02  - no  (within 12 months of item in group 2)
7      1       2016-05-05  - yes (over 12 months since last returned item in group 1)
8      1       2016-07-16  - no  (within 12 months of item in group 1)
9      2       2016-03-01  - yes (over 12 months since last returned item in group 2)

我已经使用游标（下面）制定了解决方案，但是想知道是否存在基于集合的解决方案，因为多年来这个表将增长到数百万行。

declare @lastTable table (
    groupId int not null,
    lastItemDate datetime not null
)

declare @groupId int
declare @timestamp datetime
declare @lastgroupTime datetime

declare caseCursor CURSOR for select groupId, CreatedTimestamp from #items order by CreatedTimestamp

open caseCursor

fetch from caseCursor into @groupId, @timestamp

while @@FETCH_STATUS = 0
begin
    select  @lastGroupTime = max(lastItemDate)
    from    @lastTable
    where   groupId = @groupID

    if  (@lastgroupTime is null or  dateadd(yy, 1, @lastGroupTime) < @timestamp)
    begin
        insert into @lastTable values (@groupId, @timestamp)
    end

    fetch from caseCursor into @groupId, @timestamp
end

close caseCursor
deallocate caseCursor

select * from @lastTable

Answer 1

首先选择每个组ID的最小创建日期。然后编号年份并从每个时期中选择一行。不幸的是，SQL Server在计算两个日期之间的年份并不是很好。也许365天/年的近似就足够了：

1139 - Got error 'empty (sub)expression' from regexp

根据时间窗口选择行

1 个答案: