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Thread: cardinality

  1. #1
    Join Date
    Dec 2007
    Posts
    30

    Unanswered: cardinality

    hi guys
    this might be a simple question for u guys
    what does cardinality in db2 refers?.
    i think it is usually used in analysing the visual explain.
    can some one explain how to analyse a visual explain using cardinality.

    thanks...

  2. #2
    Join Date
    Jan 2003
    Posts
    4,292
    Provided Answers: 5
    Cardinality is the number of rows. This can apply to the number of rows in the table, that match a predicate, etc. In visual explain, this is the number of rows expected to match the predicate.

    Andy

  3. #3
    Join Date
    May 2003
    Location
    USA
    Posts
    5,737
    Cardinality can also refer to the number of unique values in a column, or group of columns. In syscat.indexes, DB2 keeps stats on firstkeycard, secondkeycard, thirdkeycard, fourthkeycard, and fullkeycard to indicate the number of unique values of various columns (or combinations of columns) in an index (key).
    M. A. Feldman
    IBM Certified DBA on DB2 for Linux, UNIX, and Windows
    IBM Certified DBA on DB2 for z/OS and OS/390

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