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  1. #1
    Join Date
    Apr 2004
    Posts
    13

    Smile Pleeease...What is the cursor, index, and cluster?with an example

    I studied computer sience in the university?
    In my study we practice some SQL statements with Oracle, and SQL Server
    Also, We studied some database concepts like
    But, until now I haven't clear opinion about CLUSTERS, INDEXES, and CURSORS in the database?

    Please give an overview about them with small examples to clarify

    Thank you very much

  2. #2
    Join Date
    Jan 2004
    Location
    Europe, Finland, Helsinki
    Posts
    64

    CLUSTERS, INDEXES, and CURSORS

    Hi!

    Some fast ansvers:

    CLUSTERS - this depends very much what product you are talking. Usually this has something to do how the data is located on the disk.
    INDEXES - THE MOST INPORTANT feature in real life. Is a physical data structure, typically a b-tree. They are invisble to the SQL-queries, but have a tremendous performace issue.
    CURSORS - SQL query usually returns many rows. C, COBOL etc. 3GL-languages can read only one row a time. That's why those program languages need to define a cursor, a feature that allows program to read one row in time.

    Cheers, Bill

  3. #3
    Join Date
    May 2004
    Location
    Redwood Shores, CA
    Posts
    68
    Quote Originally Posted by hurmavi
    Hi!

    Some fast ansvers:

    CLUSTERS - this depends very much what product you are talking. Usually this has something to do how the data is located on the disk.
    INDEXES - THE MOST INPORTANT feature in real life. Is a physical data structure, typically a b-tree. They are invisble to the SQL-queries, but have a tremendous performace issue.
    CURSORS - SQL query usually returns many rows. C, COBOL etc. 3GL-languages can read only one row a time. That's why those program languages need to define a cursor, a feature that allows program to read one row in time.

    Cheers, Bill
    Bill, you probably wanted to say that if you DON'T have indexes than you will have a performance issue.

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