sql - Adding a Foreign Key to an existing Table -

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i forgot add column foreign key. tried doing following:

alter table gamestbl add console varchar(30) not null, index (console), foreign key(console) references consolestbl(consolename) on delete          cascade on update cascade;

edit:

i tried adding field first , after constraint so:

alter table gamestbl add column console varchar(30); add constraint console foreign key (console) references consolestbl(consolename);

it seems want add missing column, index, , add foreign key constraint. afaik there isn't 1 single command all in 1 go. in smaller steps :)

also, note if games table has data in it, not able add not null column without setting default.

here's 1 way this, viz adding missing column nullable, setting data, , changing not null:

(i'm assuming mysql)

alter table gamestbl add console varchar(30) null; alter table gamestbl add foreign key(console) references consolestbl(consolename) on delete cascade on update cascade; create index ix1_gamesconsole on gamestbl(console);  update gamestbl set console = 'playstation';  alter table gamestbl change column console console varchar(30) not null;

sqlfiddle here


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