Write an aggregate that finds the third largest integer in a column?
This is what i am doing:

```
create function third_step(bigint, integer) returns bigint AS
$$

SELECT distinct
 * from count_lab order by ab asc limit 1 offset 2 ;

$$ language sql; --can we use plpgsql somehow?

create aggregate third_agg(integer)
(stype=bigint,sfunc=third_step,initcond=0); 
SELECT distinct
 * from count_lab order by ab asc limit 1 offset 2  ;

```