source: database/Advanced Reports for database/List of clients who haven't made an order yet.txt@ 6c7cfa6

CREATE OR REPLACE FUNCTION get_clients_without_orders()
RETURNS TABLE (
    client_id INT,
    client_name TEXT,
    email TEXT
)
LANGUAGE plpgsql
AS $$
BEGIN
    RETURN QUERY
    SELECT
        c.client_id,
        c.name AS client_name,
        c.email
    FROM client c
    LEFT JOIN makes_order mo
        ON c.client_id = mo.client_id
    WHERE mo.order_num IS NULL
    ORDER BY c.client_id;
END;
$$;