Database: dog_kennels
Question: Which owner has paid for the most treatments on his or her dogs? List the owner id.
SQL: select t1.owner_id from owners as t1 join dogs as t2 on t1.owner_id  =  t2.owner_id join treatments as t3 on t2.dog_id  =  t3.dog_id group by t1.owner_id order by count(*) desc limit 1