Default field value in SQL query

[S3NTIN3L]

I have this query:

"SELECT member_age 
FROM members 
WHERE member_age > $age_1 
AND member_age < $age_2
AND county = '$county'
AND sex <> (SELECT sex FROM members WHERE member_id = $member_id)
AND member_id <> $member_id");

But there is an option to say "not bothered" for county in the form, therefore how would I make this query default to all counties in this case without writing another query in an if statement?

Thanks anyone

[bradgrafelman]

Build the query string in parts, and only add the 'AND country = ...' section if it's actually needed.