On Feb 4, 2005, at 12:06, Don Drake wrote:
I have a query that shows the top N count(*)'s.
So it's basically:
select some_val, count(*) from big_table group by some_val order by count(*) limit 50
Now, I would like to have the rank included in the result set. The first row would be 1, followed by 2, etc. all the way to 50.
There are a couple of different ways to go about this. One is just to append an extra column that's basically a line number, but I find it doesn't handle ties very elegantly. The following example uses a correlated subquery using HAVING to determine the rank as "the number of items that have a total quantity greater than the current item + 1". Note that items bar and baz have exactly the same totals and are tied, while the rank of bat shows that there are 3 items that have totals greater than bat.
Joe Celko's "SQL for Smarties" has a bunch of things like this in it. I've found it quite helpful.
Hope this helps.
Michael Glaesemann grzm myrealbox com
create table items ( item text not null , qty integer not null ) without oids;
insert into items (item, qty) values ('foo', 1); insert into items (item, qty) values ('foo', 2); insert into items (item, qty) values ('foo', 1); insert into items (item, qty) values ('foo', 3); insert into items (item, qty) values ('foo', 3); insert into items (item, qty) values ('foo', 20); insert into items (item, qty) values ('foo', 1); insert into items (item, qty) values ('bar', 3); insert into items (item, qty) values ('bar', 1); insert into items (item, qty) values ('bar', 3); insert into items (item, qty) values ('bar', 13); insert into items (item, qty) values ('baz', 2); insert into items (item, qty) values ('baz', 4); insert into items (item, qty) values ('baz', 14); insert into items (item, qty) values ('bat', 3); insert into items (item, qty) values ('bat', 4);
select item, sum(qty) as tot_qty from items group by item order by tot_qty desc;
item | tot_qty ------+--------- foo | 31 bar | 20 baz | 20 bat | 7 (4 rows)
select i1.item , i1.tot_qty , ( select count(*) from ( select item , sum(qty) as tot_qty from items group by item having sum(qty) > i1.tot_qty ) as i2 ) + 1 as rank from ( select item , sum(qty) as tot_qty from items group by item ) as i1 order by i1.tot_qty desc;
item | tot_qty | rank ------+---------+------ foo | 31 | 1 bar | 20 | 2 baz | 20 | 2 bat | 7 | 4 (4 rows)
---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ?
http://www.postgresql.org/docs/faq