I need to add a new column in one of my tables, but this column in turn is a foreign key from another table but I do not know how to do it ...
I tried this but evidently gave me an error:
ALTER TABLE ordenes ADD COLUMN ticket varchar(50) FOREIGN KEY (ticket) REFERENCES tickets(ticket)
First add only the column and then the fk:
ALTER TABLE ordenes ADD ticket VARCHAR(50) NOT NULL;
ALTER TABLE ordenes ADD CONSTRAINT fk_ticket FOREIGN KEY (ticket) REFERENCES tickets(ticket);
In the table tickets it would be better to call it "something" + id instead of "ticket". Remember that it has to be a unique field.
The syntax you are using is not supported by mysql. Add the column and the constraint separately, this will work in the vast majority of engines, not just MySQL:
ALTER TABLE ordenes ADD COLUMN ticket varchar(50);
ALTER TABLE ordenes ADD constraint FK_Ordenes_Tickets FOREIGN KEY (ticket) REFERENCES tickets(ticket)
I have added a name to the constraint, but you could skip that part.