在 MySQL 中创建 function

Question

I have a database of excursions, tables with information about customers, buses, drivers, bills etc. I m writing a function that calculates a payment for a specified month. But I have some mistakes and don m writing a function that calculates a payment for a specified month. But I have some mistakes and don t know how to fix them. Help me please. My function:

USE excursions_test;
DELIMITER $$
CREATE FUNCTION  sum_bill(excursion_id INT, for_begin DATE, for_end DATE) RETURNS INT
DETERMINISTIC
    BEGIN
       SELECT excStart = excursion.start_date, excEnd = excursion.end_date, excPrice =( excursion.excursion_duration*excursion.number_of_tourists*bus_model.fuel_for_km*excursion.distance)*1.5,
        IF(excStart < for_begin OR excEnd > for_end, 0, 
        IF(excStart <= for_begin OR excEnd >= for_end AND excEnd <= for_end, DATEDIFF(for_begin, excEnd)*excPrice/30,
        IF(excStart >= for_begin AND excEnd >= for_begin AND excEnd <= for_end, DATEDIFF(excStart, excEnd)*excPrice/30,
        IF(excStart >= for_begin AND excEnd >= for_end, DATEDIFF(excStart, for_end)*excPrice/30,
        IF(excStart <= for_begin AND excEnd >= for_end, DATEDIFF(for_begin, for_end)*excPrice/30, 0)))))
        FROM excursion JOIN bus_model ON excursion.bus_model_id = bus_model.bus_model_id
        WHERE excursion.excursion_id = excursion_id
        RETURN 0; -- there is a mistake
 
    END $$
    
DELIMITER ;

Answer 1

WHERE excursion.excursion_id = excursion_id <-- missing ";". It should look like this: WHERE excursion.excursion_id = excursion_id;