Re: InnoDB on delete, on update

[Victoria Reznichenko]

"Gitte und Ingolf" <brigitte.ingolf@stripped> wrote:
> Hi out there,
> 
> i.m using InnoDB with foreign key constraints and i.m looking for the
> default behavior of ON DELETE and ON UPDATE.
>
> Secondly, what does the ON UPDATE NO ACTION option means? Ist the way it is
> used in db2, that every child row must have some matching parent row. If
> this condition is not met,the Update fails and all changes are rolled back?
> Or is the Update done?

Currently NO ACTION does nothing. In a future it will work the same as RESTRICT: if you
update referenced column and there are any matching rows in the referencing table, the
update will fail.
 
> What is the meaning of ON UPDATE CASCADE and ON UPDATE SET NULL??

If you specify ON UPDATE CASCADE, every time you update row in the parent table, InnoDB
will automatically update corresponding foreign key column in all matching rows in the
child table to the same value.

ON UPDATE SET NULL means that every time you update row in the parent table, InnoDB will
automatically set corresponding foreign key column in every matching rows of the child
table to NULL.


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