Question

I have simple SQL Server query:

declare @table table (id int, name nvarchar(5), deleted bit)

insert into @table(id, name, deleted) values(1, 'A1', 0)
insert into @table(id, name, deleted) values(2, 'A1', 0)
insert into @table(id, name, deleted) values(3, 'A1', 0)
insert into @table(id, name, deleted) values(4, 'A1', 1)
insert into @table(id, name, deleted) values(5, 'A2', 0)
insert into @table(id, name, deleted) values(6, 'A2', 0)

select
    max(id) as id,
    name
from @table
where deleted = 0
group by name

it returns to rows

id  |name
--------------
3   |A1
6   |A2

but should return only one

id  |name
-------------- 
6   |A2

since last (or max) id of A1 is deleted.

How to fix my query.

Thanks a lot.

Answer 1

Since you could have a third set like this:

insert into @table(id, name, deleted) values(7, 'A3', 1)
insert into @table(id, name, deleted) values(8, 'A3', 0)

I assume you want the following returned as well, since the highest id for that name was not marked as deleted:

id    name
----  ----
8     A3

Then this query should do it:

;WITH x AS 
(
  SELECT id, name, deleted, 
    rn = ROW_NUMBER() OVER (PARTITION BY name ORDER BY id DESC)
  FROM @table
)
SELECT id = MAX(id), name 
FROM x
WHERE NOT EXISTS
(
  SELECT 1 FROM x AS x2 
  WHERE name = x.name 
  AND deleted = 1 AND rn = 1
)
GROUP BY name;

If you only want rows returned where no row for a particular name was ever deleted, then it’s slightly simpler:

SELECT id = MAX(id), name
FROM @table AS t
WHERE NOT EXISTS 
(
  SELECT 1 FROM @table 
  WHERE name = t.name AND deleted = 1
)
GROUP BY name;