add column then make foregin key mysql code example

Example 1: update foreign key value in mysql

SET foreign_key_checks = 0;
UPDATE languages SET id='xyz' WHERE id='abc';
UPDATE categories_languages SET language_id='xyz' WHERE language_id='abc';
SET foreign_key_checks = 1;

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);