Question

Lets say I have a table containing several hundred million rows that looks something like this:

memID | foo  | bar  | foobar 1     | blah | blah | blah 1     | blah | blah | blah 1     | blah | blah | blah 1     | blah | blah | blah 1     | blah | blah | blah 1     | blah | blah | blah 1     | blah | blah | blah 2     | blah | blah | blah 2     | blah | blah | blah 2     | blah | blah | blah 2     | blah | blah | blah 2     | blah | blah | blah . . . 10001 | blah | blah | blah 10001 | blah | blah | blah 

I need a query that will return the top N rows for each memID in a range of member IDs. For example, if N = 3 and the range is 0-2 it should return

memID | foo  | bar  | foobar 1     | blah | blah | blah 1     | blah | blah | blah 1     | blah | blah | blah 2     | blah | blah | blah 2     | blah | blah | blah 2     | blah | blah | blah   

I’ve considered a couple approaches, first creating a massive

SELECT TOP (3) * FROM table WHERE memID = 0 UNION ALL SELECT TOP (3) * FROM table WHERE memID = 1 . . . 

query in code. This isn’t really a realistic option for probably obvious reasons.

The second approach is to create a temporary table and loop over the range of memIDs inserting the TOP 3 for each memID into that temporary table.

WHILE @MemID < 10000 AND @MemID > 0   BEGIN     INSERT INTO tmp_Table     SELECT TOP (3) *      FROM table      WHERE memID = @MemID      SET @MemID = @MemID + 1     END 

This works, but I’m wondering if there is a more elegant single query solution that I’m missing.

Cadaeic gave me an answer that works without tinkering, but thank you to everyone that suggested analytics, it looks like I have some serious reading to do.

Answer 1

declare @startID int, @endID int, @rowsEach int select @startID = 0, @endID = 2, @rowsEach = 3   select * from (     select memID, foo, bar, foobar, row_number() over (partition by dense_rank order by dense_rank) [rank_row]     from     (         select memID, foo, bar, foobar, dense_rank() over (order by memID) [dense_rank]         from #test         where memID between @startID and @endID     ) a ) b where rank_row <= @rowsEach 

The result:

memID       foo  bar  foobar rank_row ----------- ---- ---- ------ -------------------- 1           blah blah blah   1 1           blah blah blah   2 1           blah blah blah   3 2           blah blah blah   1 2           blah blah blah   2 2           blah blah blah   3 

And here’s the set-up code if you’d like to test locally:

create table #test (       memID     int not null     , foo       char(4) not null     , bar       char(4) not null     , foobar    char(4) not null )  insert into #test (memID, foo, bar, foobar) select 1, 'blah', 'blah', 'blah' union all select 1, 'blah', 'blah', 'blah' union all select 1, 'blah', 'blah', 'blah' union all select 1, 'blah', 'blah', 'blah' union all select 1, 'blah', 'blah', 'blah' union all select 1, 'blah', 'blah', 'blah' union all select 1, 'blah', 'blah', 'blah' union all select 2, 'blah', 'blah', 'blah' union all select 2, 'blah', 'blah', 'blah' union all select 2, 'blah', 'blah', 'blah' union all select 2, 'blah', 'blah', 'blah' union all select 10001, 'blah', 'blah', 'blah' union all select 10001, 'blah', 'blah', 'blah' union all select 10001, 'blah', 'blah', 'blah'