CREATE TABLE parties (party_email VARCHAR2, party_id VARCHAR2)
CREATE TABLE party_services (customer_id VARCHAR2)

Which is the email of the party that has used the services the most number of times?
SELECT t1.party_email FROM parties AS t1 JOIN party_services AS t2 ON t1.party_id = t2.customer_id GROUP BY t1.party_email ORDER BY COUNT(*) DESC LIMIT 1
SELECT "t1"."party_email" FROM "parties" "t1" JOIN "party_services" "t2" ON "t1"."party_id" = "t2"."customer_id" GROUP BY "t1"."party_email" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY