Find Values Owned Only by the Selected User

Given a relation user_values with columns row_id, user_id, and item_value, each row records that a particular user possesses a specific text value. A user may possess the same value on multiple rows. A separate relation selected_user contains exactly one row; its single non-null integer column, user_id, identifies the user to examine. Write a read-only PostgreSQL query that returns one column named item_value. The result must contain every distinct value owned by the…