CREATE TABLE review (a_id DECIMAL, u_id DECIMAL, i_id DECIMAL, rating DECIMAL, rank DECIMAL)
CREATE TABLE trust (source_u_id DECIMAL, target_u_id DECIMAL, trust DECIMAL)
CREATE TABLE useracct (u_id DECIMAL, name TEXT)
CREATE TABLE item (i_id DECIMAL, title TEXT)

Find the number of users who did not write any review.
SELECT COUNT(*) FROM useracct WHERE NOT u_id IN (SELECT u_id FROM review)
SELECT COUNT(*) FROM "useracct" WHERE NOT "u_id" IN (SELECT "u_id" FROM "review")