I've been pulling my hair out trying to figure out how to do this. I'v created a custom field called cp_country. Now each record in Mysql has a value for cp_country. The problem is i don't understand how Wordpress indexes data into MySql.
For example look here

Normally, i'd be used to fetching rows like SELECT * FROM table WHERE cp_country='United Kingdom' But as you can see the results aren't one row, the attributes are listed by per row joined by a post id.
How do i get a results WHERE cp_country='United Kingdom'?
For example a set of results would each have cp_country,cp_street,cp_price.