Mysql Add days onto date from two different columns - mysql

Question

Hi my problem relates to adding days onto a date from two different tables in MySql in the Mamp environment.
Membership type to Membership transaction is 1 to many
The link is type_id
Date is in yyyy/mm/dd format also as this is the only format that Mamp will allow from my research.
I want a new end date column that links to the column duration from the membership type table. I want to add Duration_day onto start_date to produce an end date that matches up with the type_id. (So they link up to give the correct end date)
I want it to be automatically calculated when the start date and type-id are saved
Any help would be appreciated
Thanks

Answer 1

You will need a trigger on INSERT/UPDATE - a calculated column (for MySQL v5.7.6+) will not work in your case (it can only refer to columns in the same table).
The 2 triggers may look like this
CREATE DEFINER = 'root'#'%' TRIGGER `m_duration_ins_tr1` BEFORE INSERT ON `membership`
FOR EACH ROW
BEGIN
DECLARE duration INTEGER;
SELECT m_duration INTO duration FROM membership_type WHERE id = NEW.type_id;
SET NEW.end_date := DATE_ADD(NEW.start_date, INTERVAL duration DAY);
END;
CREATE DEFINER = 'root'#'%' TRIGGER `m_duration_ins_tr1` BEFORE UPDATE ON `membership`
FOR EACH ROW
BEGIN
DECLARE duration INTEGER;
SELECT m_duration INTO duration FROM membership_type WHERE id = NEW.type_id;
SET NEW.end_date := DATE_ADD(NEW.start_date, INTERVAL duration DAY);
END;