Question

请帮我弄清楚以下逻辑。当B.DateTime与E.DateTime匹配时，获得E.Location。当B.DateTime＆lt;＆gt; E.DateTime，然后从之前/之前的E.DateTime获得E.Location。请在（＆＃39;城市A＆＃39;，＆＃39;城市B＆＃39;，＆＃39;城市C＆＃39;，＆＃39;城市E＆＃39;，＆＃39;城市F＆＃39;城市G＆＃39;城市X＆＃39;城市Y＆＃39;）。我将感激你。这是sqlfiddle：http://sqlfiddle.com/#!6/8eb014/1

Base table as B
Id   DateTime
201  2015-05-03 08:01
301  2015-05-03 08:20
401  2015-05-03 08:40

Extract Table as E
Id   DateTime            Location
201  2015-05-03 07:50    City A
201  2015-05-03 08:01    City B
201  2015-05-03 08:50    City C
301  2015-05-03 07:15    City E
301  2015-05-03 08:01    City F
301  2015-05-03 08:20    City G
401  2015-05-03 07:15    City X
401  2015-05-03 08:55    City Y

Desired Result:
Location  Id    DateTime
City B    201   2015-05-03 08:01
City G    301   2015-05-03 08:20
City X    401   2015-05-03 07:15

我在sqlfiddle上尝试了以下代码，但执行起来有问题：

select B.id, coalesce(E.Location,F.Location),coalesce(E.DateTime,F.DateTime)
from Base B
inner join Extract E
on B.id = E.id
and B.DateTime = E.DateTime
and E.Location in ('City A','City B','City C','City E','City F','City G','City X','City Y')
left join Extract F
on B.id = F.id
and F.DateTime < B.DateTime
and F.Location in ('City A','City B','City C','City E','City F','City G','City X','City Y')

当我使用我的实际数据运行此逻辑时，我得到以下结果。

Location  Id    DateTime
City B    201   2015-05-03 08:01
City G    301   2015-05-03 08:20

Id 401错过了。

Answer 1

试试这个。它将通过首先匹配日期然后按日期排序：

select B.id, ca.dt, ca.location
from B
cross apply(select top 1 location, dt
            from E 
            where B.id = E.id 
            order by case when B.dt = E.dt then 1 else 0 end desc,
                     E.dt)ca

Answer 2

请尝试以下查询。您正在使用B和E上的内部联接，它会在日期时间字段中过滤掉401，因为e没有它。

select distinct b.id,coalesce(e.location,a.location) ,coalesce(e.datetime,a.dt)
from base b
left outer join extract e 
on b.id = e.id
and b.datetime = e.datetime
and E.Location in ('City A','City B','City C','City E','City F','City G','City X','City Y')
inner join 
(
select b2.id,f.location,max(f.datetime) as dt from base b2 join extract f on b2.id = f.id and b2.datetime <> f.datetime
where f.datetime < b2.datetime
group by b2.id,f.location 
) a
on b.id = a.id

通过匹配和不匹配的DateTime记录

2 个答案: