使用分组子句时如何避免重叠的日期范围？

问题描述

sql SERVER ISLANDS按照@KM的建议进行研究后，我想到了以下查询，当向数据集中添加其他类代码时，此查询似乎运行良好。

select a.code, a.class, a.txdate as mindate, b.txdate as maxdate
from (
    --Find minimum island
    select code
        , class
        , txdate
        , row_number() over (order by code, class, txdate) as n
    from #items tb1
    where not exists (
        select *
        from #items tb2
        where datediff(d, tb1.txdate, tb2.txdate) = -1      
          and tb1.class = tb2.class
          and tb1.code = tb2.code
    ) 
) as a
inner join (
    --Find maximum island 
    select code
        , class
        , txdate
        , row_number() over (order by code, class, txdate) as n
    from #items tb1
    where not exists (
        select *
        from #items tb2
        where datediff(d, tb1.txdate, tb2.txdate) = 1   
          and tb1.class = tb2.class
          and tb1.code = tb2.code
    ) 
) as b on a.n = b.n

此方法的唯一警告是，最小集合中的条目数需要与最大集合中的条目数匹配。到目前为止，我还无法做任何使这不成立的事情。但是，我没有测试空值或性能。

解决方法

我有一种情况，我需要查找值更改之间的时间跨度。我尝试了一个简单的group by子句，但它消除了重叠的更改。考虑以下示例：

create table #items (
      code varchar(4),class varchar(4),txdate datetime
)

insert into #items (code,class,txdate) values ('A','C','2010-01-01');
insert into #items (code,'2010-01-02');
insert into #items (code,'2010-01-03');
insert into #items (code,'D','2010-01-04');
insert into #items (code,'2010-01-05');
insert into #items (code,'2010-01-06');
insert into #items (code,'2010-01-07');
insert into #items (code,'2010-01-08');
insert into #items (code,'2010-01-09');

select code,min(txdate) mindate,max(txdate) maxdate
from #items
group by code,class

这将返回以下结果（请注意重叠的日期范围）：

|code|class|mindate   |maxdate   |
----------------------------------
|A   |C    |2010-01-01|2010-01-07|
|A   |D    |2010-01-04|2010-01-09|

我希望查询返回以下内容：

|code|class|mindate   |maxdate   |
----------------------------------
|A   |C    |2010-01-01|2010-01-03|
|A   |D    |2010-01-04|2010-01-05|
|A   |C    |2010-01-06|2010-01-07|
|A   |D    |2010-01-08|2010-01-09|

有什么想法和建议吗？

sql sql