I am not up to scratch with innodb, but in oracle
you would have a Primary key on both the id fields in the Car and person
table and a Foreign key on PersonId linking it to Id in the Person table.
IN your select an index on PersonId would be beneficial if the tables get
large.
Jack
2008/10/2 J Hussein <[EMAIL PROTECTED]>
> Hi,
>
> I'm slightly confused about foriegn keys and indexes on mysql innodb
> tables.
> Foreign key constraints create a reference between two tables and indexes
> make queries on a particular table faster if the index is on a field in the
> where or order by clause.
>
> My question was whether say for the following two tables:
>
> Person Car
>
> Id Id
> Name PersonId
> Address Make
> Phone Number Colour
>
> If I create a foriegn key linking the id field in person and the personid
> field in car, do I need to create another index in car table specifically
> for the personid field if I was running a query such as:
>
> "SELECT Id FROM car WHERE personid={personkeynumber}"?
>
> Thanks for your help.
>
> Jemma
>
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