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* column label
@ 2003-03-21 20:55 Ryan <pgsql-sql@seahat.com>
0 siblings, 1 reply; 4+ messages in thread
From: Ryan @ 2003-03-21 20:55 UTC (permalink / raw)
To: pgsql-sql
Ok I have a query in a program that looks something like this
select
reference_number as foo,
'(10,10)'::point <-> point(x,y) as distance
from imagemap
where
index_number = '2322' and
block_number = '140'
order by distance
limit 1;
I wanted to add a clause in where 'and distance < 30'
but according to the postgres manual it says I cannot do that for WHERE or
HAVING clauses, instead use the real name.
However dropping the 'as distance' from my query gives me a column name of
'?column?' which happens to not be worth a dang thing.
How can it be done?
(I suddenly have a feeling its going to require a subselect)
Ryan
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: column label
@ 2003-03-24 09:33 Tomasz Myrta <jasiek@klaster.net>
parent: Ryan <pgsql-sql@seahat.com>
0 siblings, 1 reply; 4+ messages in thread
From: Tomasz Myrta @ 2003-03-24 09:33 UTC (permalink / raw)
To: Ryan <pgsql-sql@seahat.com>; +Cc: pgsql-sql
Uz.ytkownik Ryan napisa?:
> Ok I have a query in a program that looks something like this
>
> select
> reference_number as foo,
> '(10,10)'::point <-> point(x,y) as distance
> from imagemap
> where
> index_number = '2322' and
> block_number = '140'
> order by distance
> limit 1;
>
> I wanted to add a clause in where 'and distance < 30'
> but according to the postgres manual it says I cannot do that for WHERE or
> HAVING clauses, instead use the real name.
>
> However dropping the 'as distance' from my query gives me a column name of
> '?column?' which happens to not be worth a dang thing.
>
> How can it be done?
>
> (I suddenly have a feeling its going to require a subselect)
Your feeling is 50% accurate. If you want to use subselect, throw "<10"
into this subselect, because you will have performance loss.
You can also use whole function in where clause and order by:
select
reference_number as foo,
'(10,10)'::point <-> point(x,y) as distance
from imagemap
where
index_number = '2322' and
block_number = '140'
where '(10,10)'::point <-> point(x,y)<10
order by '(10,10)'::point <-> point(x,y)
limit 1;
BTW Did you try to use polygons in your image maps, or you have rather
point oriented web page than area oriented?
Regards,
Tomasz Myrta
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: column label
@ 2003-03-25 14:50 Ryan <pgsql-sql@seahat.com>
parent: Tomasz Myrta <jasiek@klaster.net>
0 siblings, 0 replies; 4+ messages in thread
From: Ryan @ 2003-03-25 14:50 UTC (permalink / raw)
To: jasiek@klaster.net; +Cc: pgsql-sql
> Uz.ytkownik Ryan napisa?:
>> Ok I have a query in a program that looks something like this
>>
>> select
>> reference_number as foo,
>> '(10,10)'::point <-> point(x,y) as distance
>> from imagemap
>> where
>> index_number = '2322' and
>> block_number = '140'
>> order by distance
>> limit 1;
>>
>> I wanted to add a clause in where 'and distance < 30'
>> but according to the postgres manual it says I cannot do that for
>> WHERE or HAVING clauses, instead use the real name.
>>
>> However dropping the 'as distance' from my query gives me a column
>> name of '?column?' which happens to not be worth a dang thing.
>>
>> How can it be done?
>>
>> (I suddenly have a feeling its going to require a subselect)
> Your feeling is 50% accurate. If you want to use subselect, throw "<10"
> into this subselect, because you will have performance loss.
>
> You can also use whole function in where clause and order by:
> select
> reference_number as foo,
> '(10,10)'::point <-> point(x,y) as distance
> from imagemap
> where
> index_number = '2322' and
> block_number = '140'
> where '(10,10)'::point <-> point(x,y)<10
> order by '(10,10)'::point <-> point(x,y)
> limit 1;
>
> BTW Did you try to use polygons in your image maps, or you have rather
> point oriented web page than area oriented?
>
> Regards,
> Tomasz Myrta
Thats kind of a pain... I'd rather perform the calculation once and then
do my order and where on the one value. Is there any reason why postgres
does not recognize labels under WHERE?
The reason I use points is because my customized web-based image
mapping/ocr program can deal with points very aptly. Also with a distance
based calc overlap is not really an issue as with polygons. The reason I
am trying to limit the distance is simply to cut out clicking on far away
parts of the image. Heck, I could check distance on the program side of
things but I try and keep as much in SQL as possible.
Ryan
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: column label
@ 2003-03-26 09:55 Christoph Haller <ch@rodos.fzk.de>
0 siblings, 0 replies; 4+ messages in thread
From: Christoph Haller @ 2003-03-26 09:55 UTC (permalink / raw)
To: pgsql-sql; +Cc: pgsql-sql@seahat.com
> >> Ok I have a query in a program that looks something like this
> >>
> >> select
> >> reference_number as foo,
> >> '(10,10)'::point <-> point(x,y) as distance
> >> from imagemap
> >> where
> >> index_number =3D '2322' and
> >> block_number =3D '140'
> >> order by distance
> >> limit 1;
> >>
> >> I wanted to add a clause in where 'and distance < 30'
> >> but according to the postgres manual it says I cannot do that for
> >> WHERE or HAVING clauses, instead use the real name.
> >>
> >> However dropping the 'as distance' from my query gives me a column
> >> name of '?column?' which happens to not be worth a dang thing.
> >>
> >> How can it be done?
> >>
> >> (I suddenly have a feeling its going to require a subselect)
> > Your feeling is 50% accurate. If you want to use subselect, throw
"<10"
> > into this subselect, because you will have performance loss.
> >
> > You can also use whole function in where clause and order by:
> > select
> > reference_number as foo,
> > '(10,10)'::point <-> point(x,y) as distance
> > from imagemap
> > where
> > index_number =3D '2322' and
> > block_number =3D '140'
> > where '(10,10)'::point <-> point(x,y)<10
> > order by '(10,10)'::point <-> point(x,y)
> > limit 1;
> >
> Thats kind of a pain... I'd rather perform the calculation once and
then
> do my order and where on the one value. Is there any reason why
postgres
> does not recognize labels under WHERE?
>
So how about
select foo, distance from (
select
reference_number as foo,
'(10,10)'::point <-> point(x,y) as distance
from imagemap
where
index_number = '2322' and
block_number = '140'
) as bar
where distance < 30
order by distance
limit 1;
The reason why postgres does not recognize labels under WHERE
is the WHERE clause is evaluated before column aliasing takes place.
But there is this valuable feature of using a sub-SELECT as
from_item, so this should not be a problem at all.
Alternatively you could use
select
reference_number,
'(10,10)'::point <-> point(x,y)
from imagemap alias (foo, distance)
where
index_number = '2322' and
block_number = '140' and distance < 30
order by distance
limit 1;
Does this help?
Regards, Christoph
^ permalink raw reply [nested|flat] 4+ messages in thread
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2003-03-21 20:55 column label Ryan <pgsql-sql@seahat.com>
2003-03-24 09:33 ` Tomasz Myrta <jasiek@klaster.net>
2003-03-25 14:50 ` Ryan <pgsql-sql@seahat.com>
2003-03-26 09:55 Re: column label Christoph Haller <ch@rodos.fzk.de>
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