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  1. #1
    Join Date
    Sep 2011
    Posts
    71

    Post Unanswered: difference is between using SET and SELECT when assigning varaibles in T-SQL?


    Do you know what the difference is between using SET and SELECT when assigning varaibles in T-SQL? Well, there are some differences. I came across a great article by Narayana Vyas Kondreddi from the UK that describes the difference between the two.

    The article is well worth the read, but here are the main points:

    SET is the ANSI standard for variable assignment, SELECT is not.
    SET can only assign one variable at a time, SELECT can make multiple assignments at once.
    If assigning from a query, SET can only assign a scalar value. If the query returns multiple values/rows then SET will raise an error. SELECT will assign one of the values to the variable and hide the fact that multiple values were returned (so you'd likely never know why something was going wrong elsewhere - have fun troubleshooting that one)
    When assigning from a query if there is no value returned then SET will assign NULL, where SELECT will not make the assignment at all (so the variable will not be changed from it's previous value)
    As far as speed differences - there are no direct differences between SET and SELECT. However SELECT's ability to make multiple assignments in one shot does give it a slight speed advantage over SET.

    Take a look at the complete article to see Vyas' complete tests to get the entire picture:
    [http://vyaskn.tripod.com/differences...nd_select.htm]

    Originally written by Rayan Fairely
    T-SQL: SET vs SELECT when assigning variables

  2. #2
    Join Date
    Nov 2004
    Posts
    1,427
    Provided Answers: 4
    Paultech,

    Last SQL Server restart, Performance monitoring, Database object documentation, SET vs SELECT. I like your initiative a lot!

    Looking forward for more of this.
    With kind regards . . . . . SQL Server 2000/2005/2012
    Wim

    Grabel's Law: 2 is not equal to 3 -- not even for very large values of 2.
    Pat Phelan's Law: 2 very definitely CAN equal 3 -- in at least two programming languages

  3. #3
    Join Date
    Sep 2011
    Posts
    71

    Lightbulb

    Quote Originally Posted by Wim View Post
    Paultech,

    Last SQL Server restart, Performance monitoring, Database object documentation, SET vs SELECT. I like your initiative a lot!

    Looking forward for more of this.
    OK Wim I like that
    Thanks for your good notice ,I appreciated it too much

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