如何选择不同的数据？

Question

I'm new in SQL and I this for my uni project. I have a table with columns Rego, FirstRego, LastRego, RegoDue .

Suppose I have the following data:

  Rego      FirstRego                      LastRego                      RegoDue
YGF 615 2011-04-07 00:00:00.000 2011-04-07 00:00:00.000 2012-04-07 00:00:00.000
YGF 615 2011-04-07 00:00:00.000 2012-04-07 00:00:00.000 2013-04-07 00:00:00.000
ZIR 377 2012-10-05 00:00:00.000 2012-10-05 00:00:00.000 2013-10-05 00:00:00.000
ZIR 377 2012-10-05 00:00:00.000 2013-10-05 00:00:00.000 2014-10-05 00:00:00.000
ZJT 795 2012-10-31 00:00:00.000 2012-10-31 00:00:00.000 2013-10-31 00:00:00.000
ZSU 823 2012-04-30 00:00:00.000 2012-04-30 00:00:00.000 2013-04-30 00:00:00.000

In the query output I want the Rego to be once with the highest RegoDue ie the output should look like:

Rego      FirstRego                      LastRego                      RegoDue
YGF 615 2011-04-07 00:00:00.000 2012-04-07 00:00:00.000 2013-04-07 00:00:00.000
ZIR 377 2012-10-05 00:00:00.000 2013-10-05 00:00:00.000 2014-10-05 00:00:00.000
ZJT 795 2012-10-31 00:00:00.000 2012-10-31 00:00:00.000 2013-10-31 00:00:00.000
ZSU 823 2012-04-30 00:00:00.000 2012-04-30 00:00:00.000 2013-04-30 00:00:00.000

How can I do this?

Answer 1

Select * 
From Tbl T1
Where RegoDue =
(
    Select Max(RegoDue)
    From Tbl T2
    Where T2.Rego = T1.Rego
)

Answer 2

Firstly you want to find the latest rego due date. Once you have this you can join on it to filter out the undesired results.

select
    t.Rego, t.FirstRego, t.LastRego, lr.LatestRegoDue as RegoDue
from Table1 t
    join
    (
        select
           Rego, max(RegoDue) as LatestRegoDue
        from Table1
        group by Rego
    ) lr on t.Rego = lr.Rego and t.RegoDue = lr.LatestRegoDue