mysql add constraint foreign key syntax code example

Example 1: mysql alter add foreign key

ALTER TABLE ordenes ADD ticket VARCHAR(50) NOT NULL;
ALTER TABLE ordenes ADD CONSTRAINT fk_ticket FOREIGN KEY (ticket) REFERENCES tickets(ticket);

Example 2: foreign key type uniqu mysql

mysql > create unique index index_bar_id on foos(bar_id);
mysql > alter table foos add constraint index_bar_id foreign key (bar_id) references bars (id);