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Limitations on tables w/o primary keys

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  • Limitations on tables w/o primary keys

    Hi,

    Just noticed that :-

    "DELETE operation is unsupported on tables without primary key. Also rows in tables without primary key may appear in different order on different nodes. As a result SELECT...LIMIT... may return slightly different sets."

    has been removed from http://www.percona.com/doc/percona-x...imitation.html but is still present in the pdf manual. Has that limitation been removed and the pdf not yet updated or is the web page wrong?

    Thanks

    Ben

  • #2
    This limitation was lifted when this feature was added: http://www.percona.com/doc/percona-x..._certify_nonPK

    However, it's still generally a best practice to have explicit PKs. If you don't define them, then you will have in implicit hidden 6-byte PK in your Innodb table taking up space that you can't use for any querying. Innodb is very much optimized towards PK lookups, so it benefits you to have one you can query by.

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