Question

Consider a table with the following schema:

id, location, starred

There are many records with the same location:

id | location | starred
-----------------------
1     rome      yes
2     rome      no
3     rome      no
4     milan     yes
5     milan     no
6     bozen     no

I want to have at most one record per location. And given the choice between a starred record and a not starred record I want the starred.
So what sql will produce this table:

id | location | starred
-----------------------
1     rome      yes
4     milan     yes
6     bozen     no

I suspect this could be done with some virtual tables or ªviews’.

DELETE FROM table
GROUP BY location, 

Answer 1

If [started] can only be yes, or no, then this should work:

create table data
(
id int identity(1,1),
location varchar(50),
[started] varchar(3)
)

insert into data select 'Rome', 'Yes'
insert into data select 'Rome', 'No'
insert into data select 'Rome', 'No'
insert into data select 'Milan', 'Yes'
insert into data select 'Milan', 'No'
insert into data select 'Bozen', 'No'

WITH locationsRanked (id, location, [started], rank)
AS
(
    select min(Id), location, [started],
    RANK() OVER (PARTITION BY location  ORDER BY location, [started] DESC) AS Rank
    from data
    group by location, [started]
)
select * from locationsRanked where Rank = 1
order by id