MySQL Trigger Update with select from another table

Just learning about triggers and I'm created the following trigger;

CREATE TRIGGER `incremental_before_ins_tr` BEFORE INSERT ON incremental`
FOR EACH ROW
BEGIN
SET NEW.source = (Select source from crm_record
where msisdn = new.msisdn order by dat DESC limit 1);
END;

However the value does not appear to be getting updated. Any ideas?

I've actually managed to solve this myself. Here is the updated code

CREATE TRIGGER `incremental_before_ins_tr` BEFORE INSERT ON `incremental`
FOR EACH ROW
BEGIN
SET NEW.source = (Select source from crm_record
where crm_record.msisdn = new.msisdn order by dat DESC limit 1);
END;

I needed to specify the table name prior to the column value on line 5.

Looks like you have a typo.

You have entered incremental with a trailing backtick instead of enclosing it in backticks.

It is likely that your trigger is now bound to a table called incremental` which I am assuming does not exist.

Since you have ruled out the above. I see that the UPDATE keyword is missing. Add UPDATE table before your SET line. Replace table with the name of your table.