>> >> On Sat, Dec 1, 2012 at 8:09 AM, Leonardo M. Ramé
>> <[1][1]l.rame@...>
>> >> wrote:
>> >>
>> >> > Hi, I'm wondering if there's a way to refer columns by number in
>> WHERE
>> >> > conditions.
>> >> >
>> >> > I need this because I'm creating a generic method to create where
>> >> > clauses for hopefully ANY query, in FreePascal
>> >>
>> >> What you suggest, sir, is blasphemy. One of the major creeds of
>> relational
>> >> theory is the separation of the logical from the physical. Codd and all
>> >> his minions will strike you down.
>> >>
>> >> On the other hand, why not just use consistent aliases?
>> >>
>> >> select
>> >> case
>> >> when (a.IDADICIONAL is null) then 'TITULAR'
>> >> else 'ADICIONAL'
>> >> end as col1,
>> >> c.idcliente as col2, c.apellido as col3, c.nombres as col4
>> >> from clientes c
>> >> left join adicionales a on a.IDADICIONAL = c.IDCLIENTE
>> >>
>> >> >
>> >> >
>> >
>> > Ann, column name is not the problem. What I wanted to do is to use the
>> > alias in the WHERE clause, there's no solution for this in a simple
>> > select.
>>
>> You can use a derived table.
>>
>
> Yes Thomas, I ended up using a derived table.
>
> I have one doubt regarding derived tables. Imagine an inner query that
> returns millions of records, and the outer table with a where clause that
> limits the results to just a few records, how this affects to
> server performance?.

I don't have an answer out-of-the box, but this can be easily checked by
inspecting the execution plan and I/O statistics.


--
With regards,
Thomas Steinmaurer
http://www.upscene.com/