On Oct 17, 2008, at 12:30 PM, Kynn Jones wrote:
> Suppose I have two table X and Y and I want to compute the ratio of
> the number of rows in X and the number of rows in Y. What would be
> the SQL I could type into a psql session to get this number?
>
> This is an example of the recurring problem of performing arithmetic
> using the result of various calls to count(*) (or other mathematic
> functions).
select (select count(*)::float from X) / (select count(*)::float from
Y);
count(*) may take a while on large tables; there are other options if
you'd prefer something fast and approximate.
Cheers,
Steve