time calculations - Mailing list pgsql-admin

Hi,

I've got a table with two columns: one for distance in km (float4) and
one for the time (interval). I'd like to calculate the speed.

My problem is how to convert the intervals to decimal hours to be able
to a simple:

SELECT *, distance/time as speed from table;

Any clues? Are there any docs (maybe I have overseen something)?

Regards,
Oliver