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Increasing the values in a column

  • July 9, 2009 at 5:19 pm

    #134181

    Hi,

    I am a novice to T-SQL and I believe I am not fully harnessing the power of SQL when I find my code full of loops and conditional statements, I am hoping you folks can point me in the right direction.

    Here is the table I have,

    CREATE TABLE tableA

    (

    id INT primary key,

    year CHAR(10)

    data CHAR(100) )

    What I am trying to do is to add a constant number to values of the year column for all matching rows. e.g. change all the years to 4 year later by adding 4 to the year column.

    Is there a easy way to do this instead of pulling each row out and adding 1 to every row?

    Thanks in advance for any help

  • July 9, 2009 at 5:24 pm

    #1022784

    UPDATE dbo.tablea SET Year = CONVERT( int, Year ) + 1

    I am counting on a number of facts here, I converted it to an integer, it will convert it back to a varchar for me. I also count on the fact that I want to change ALL records. If I don't I need a WHERE clause to restrict it.

    Clear?

    CEWII

  • July 9, 2009 at 5:47 pm

    #1022794

    I added a where clause and it worked perfectly, I'm sure glad to throw out all the control statements and loops. Thanks a lot Elliott!

  • July 9, 2009 at 6:00 pm

    #1022800

    You are welcome, this is called a SET based operation, you performed the operatio on a whole set instead RBAR (Row-by-agonizing-row)..

    CEWII

  • July 10, 2009 at 6:59 am

    #1022998

    That being said, you should be careful about doing an update on a large number of rows, in a production database, since the operation will lock the rows that are being updated, and other operations against those rows will timeout until the update is complete. In the case of a simple update like yours, it's probably not an issue, but if your update would take a long time to run, you could risk losing other data in the process. If that's the case, then the approach of updating one record at a time is probably the better one, despite looking ugly.

  • July 19, 2009 at 9:50 pm

    #1026710

    kramaswamy (7/10/2009)

    If that's the case, then the approach of updating one record at a time is probably the better one, despite looking ugly.

    Ummm... no... not if it's done correctly. Correctly means that you know the updates are prequalified and will work without failure.

    --Jeff Moden

    RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
    First step towards the paradigm shift of writing Set Based code:
    ________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

    Change is inevitable... Change for the better is not.

    Helpful Links:
    How to post code problems
    How to Post Performance Problems
    Create a Tally Function (fnTally)

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