CREATE TABLE branch (branch_id NUMBER, name CLOB, open_year CLOB, address_road CLOB, city CLOB, membership_amount CLOB)
CREATE TABLE purchase (member_id NUMBER, branch_id CLOB, year CLOB, total_pounds NUMBER)
CREATE TABLE membership_register_branch (member_id NUMBER, branch_id CLOB, register_year CLOB)
CREATE TABLE member (member_id NUMBER, card_number CLOB, name CLOB, hometown CLOB, level NUMBER)

Show the membership level with most number of members.
SELECT level FROM member GROUP BY level ORDER BY COUNT(*) DESC LIMIT 1
SELECT "level" FROM "member" GROUP BY "level" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY