Re: [SQL] problem with select

Holm Tiffe ha scritto:

> Tom Lane wrote:
>
> > Holm Tiffe <holm@freibergnet.de> writes:
> > > What I try to find is a solution for a search in this table like this:
> >
> > > select distinct code,category from products where code ~* 'abc' or
> > > category ~* 'abc' or manufacturer ~* 'abc' or description ~* 'abc'
> > > or comment ~* 'abc' order by code;
> >
> > > So far so good, but I have the problem that I have the value 'abc'
> > > only one times !
> >
> > How about
> >
> > select distinct code,category from products where
> > (code || category || manufacturer || ...) ~* 'abc';
> >
> > Actually you'd probably want to also concatenate some separator markers,
> > maybe (code || '|' || category || ...), so that you didn't get bogus
> > matches across fields, like where code ends in 'a' and category starts
> > with 'bc'.
> >
> > Note that this select will be a bit of a memory hog because
> > text-slinging is very wasteful of space in 6.5 (the intermediate results
> > from the concatenate operators don't get freed till end of transaction).
> > So it might not be workable if you have a large database.  I hope to see
> > that fixed for 6.6 or 6.7.
> >
> >                       regards, tom lane
>
> Hm, clever.
>
> It is almost working, my database isn't that big that memory becomes a
> problem; the machine has 512MB.
>
> But why is nothing found if one value of a column contains NULL ?
>
> select distinct code,category from products where (code || '|' || category
>  || '|' || comment || '|' || description || '|' || desc_de) ~* 'kde';
>   code|category
> ------+--------
> 06-001|KDE
> (1 row)
>
> shop=> update products set comment = Null where code ='06-001';
> UPDATE 1
> shop=> select (comment || '|' || code) from products where code ~* '06-001';
> ?column?
> --------
>
>

Try using the COALESCE function:

select distinct code,category from products where (code || '|' ||
coalesce(category,' ') || '|' || coalesce(comment,' ') || '|' ||
coalesce(description,' ') || '|' || coalesce(desc_de,' ')) ~* 'kde';

José