alter table create foreign key mysql code example
Example: 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);
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);