-- Create sequence for sales order numbers
CREATE SEQUENCE so_number_seq START WITH 1 INCREMENT BY 1;

CREATE OR REPLACE FUNCTION generate_so_number()
RETURNS VARCHAR AS $$
DECLARE
    next_val INTEGER;
BEGIN
    next_val := nextval('so_number_seq');
    RETURN 'SO-' || LPAD(next_val::TEXT, 5, '0');
END;
$$ LANGUAGE plpgsql;