[Koha] Look for records with specific info in a mark field

Hi How can I do a MySQL search for all the records/items with an specific value in an specific marc field Xx? I've looked at the bilblio and related tables but I'm unable to find a table with marcs fields info. I saw some marcxml fields however; are marc values stored there and I need to xlmparse that info to get an specific value? Regards Alvaro