Re: Determining Rank - Mailing list pgsql-sql

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)