drop sequence train_info_id_seq;
create sequence train_info_id_seq;
 
drop table train_info;
create table train_info (
        train_info_id   integer default nextval('train_info_id_seq'),
        train_number    varchar(20) not null,
        leaves          time,
        arrives         time,
        primary key (train_info_id)
);
 
 
create or replace function add_train(train_no text,depart time,arrival time)
 
        returns void as '
BEGIN
        LOOP
                update train_info set train_number = train_no
                where train_number = train_no ;
                IF found THEN
                        RETURN;
                END IF;
                insert into train_info(train_number,leaves,arrives)
                values ( train_no,depart,arrival);
                RETURN;
 
 
        END LOOP;
END;
' language 'plpgsql';