From: Peter Brawley
Date: August 10 2005 4:32pm
Subject: Re: SELECT vs SET for creating variables
List-Archive: http://lists.mysql.com/mysql/187622
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Bill,

 >SELECT @neededStep := 10;
 >SELECT @startOfCenter := 7;
 >SELECT @returnData :=
 >IF(@neededStep <= @startOfCenter,
 >     CONCAT(@neededStep, ' <= ', @startOfCenter),
 >     CONCAT(@neededStep, ' > ', @startOfCenter)
 >    );

 >In the above example @returnData ends up being '10 <= 7', but when 
@neededStep
 >is less than 10 the expected results are found. (could this be because 
@neededStep
 >is stored as text and not a number?)

In 5.0.10, @returndata is '10 > 7';

PB

-----

Bill Dodson wrote:

> I am using version 4.0.12-nt on a Windows 2000 machine.
>
> I have noticed some difference in the way SET and SELECT create 
> variables.  The following statements do not work the way I would expect.
>
> SELECT @neededStep := 10;
> SELECT @startOfCenter := 7;
> SELECT @returnData :=
> IF(@neededStep <= @startOfCenter,
> CONCAT(@neededStep, ' <= ', @startOfCenter),
> CONCAT(@neededStep, ' > ', @startOfCenter)
> );
>
> In the above example @returnData ends up being '10 <= 7', but when 
> @neededStep is less than 10 the expected results are found. (could 
> this be because @neededStep is stored as text and not a number?)
>
> In the next example @returnData ends up being '10 > 7', as expected.  
> This seems to work for all values of @neededStep I have tested.
>
> SET @neededStep := 10;
> SET @startOfCenter := 7;
> SELECT @returnData :=
> IF(@neededStep <= @startOfCenter,
> CONCAT(@neededStep, ' <= ', @startOfCenter),
> CONCAT(@neededStep, ' > ', @startOfCenter)
> );
>
> It would seem that SET is a better way to create variables from 
> constant values, but I would like to understand why.  Does anybody 
> know what is happening here?
>
> Thanks for your time!
> bill
>


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