read hostname only from domain values

can regexp be used before where

[phparion]

hi

I have table which has a column called URL, in which different formats of urls are stored.

I want to read hostname, www.domain.com, from url column and strip out remaining data.

I was reading regexp manual and i think it cannot be use before WHERE clause e.g

select url regexp '' from table

but at the same time i saw this functionality on another website so it is doable. can anybody guide me please how to do this?

thank you