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


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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J.A. van Zanen

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