NYCPHP Meetup

[Stephen Musgrave]

Thank you all for your suggestions... I'll digest and dive in...  
again... thanks!!!


On Mar 21, 2006, at 12:04 PM, Michael Sims wrote:

> On Tuesday 21 March 2006 11:28, Stephen Musgrave wrote:
>
>> The almighty list:
>>
>> I am struggling with including a field returned from the subselect in
>> the WHERE clause of the parent SELECT.  I keep on getting an error
>> that the field is unknown:
>>
>> "Unknown column 'pt_prgm_term_overall_end_date' in 'where clause'"
>>
>> I have seen that this is a bug in previous versions of MySQL, but I
>> am using 4.1.18 and it was to have been fixed by this version, 4.1.16
>> I believe.
>
> Can't do it.  No aliases in WHERE statement.  Put it in HAVING  
> instead, and
> it will work.
>
> http://dev.mysql.com/doc/refman/4.1/en/problems-with-alias.html
>
> Think of it this way: when it does the WHERE, it's trying to figure  
> out
> what rows should be included in the results - a first stab at the  
> problem.
> It hasn't even looked at the SELECT part of the statement yet -  
> once it
> figures out what rows should be included overall, then it'll take a  
> look
> at the SELECT fields to decide which columns from those rows it needs.
> And THEN, only then, will it look at the HAVING section - a last  
> stab at
> winnowing the result set.
>
> So: if you want to eliminate unwanted results early (to make queries
> quicker), put the condition early in the WHERE clause.  If you want to
> eliminate unwanted results late (because you're doing something  
> tricksy),
> put it in the HAVING clause.
>
>
> Michael Sims
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