Re: user variable ist not assigned when using function like SUM(), MAX(), AVG()

[email protected] wrote:
> Hello,
> 
> this is may first bug report so I don't really know exactly what and how to
> tell ...
> 
> The bug appears in all tested versions:
> 4.0.12-nt/Windows 2000 prof. SP4
> 4.0.15/Linux/SuSE
> 4.0.17-nt/Windows XP prof. SP1
> 4.0.20-nt/Windows 2000 prof. SP4
> 5.0.00-alpha/Windows XP prof. SP1
> 
> User variables are assigned correctly with
>     SELECT @var := value;
> 
> This fails when one of the the following functions is used
>     MIN(), MAX(), SUM(), AVG(), COUNT() ...
>     

This is documented behaviour, see

    http://dev.mysql.com/doc/mysql/en/Variables.html

    [...]

    Note: In a SELECT statement, each expression is evaluated only
    when sent to the client. This means that in a HAVING, GROUP BY,
    or ORDER BY clause, you cannot refer to an expression that
    involves variables that are set in the SELECT list.

    [...]

    The general rule is to never assign and use the same variable
    in the same statement.

    [...]

-- 
Hartmut Holzgraefe  <[email protected]>

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