Re: Question about fulltext search and to_tsvector function

Mike,

1. always separate attributes by blank unless you sure words can span different
   columns, e.g., title||' '||description
2. use coalesce to avoid unexpected NULL string

Oleg

On Thu, 16 Oct 2008, Mike Christensen wrote:

> Okay this one's driving me crazy.
>
> Should there be any difference between the following queries:
>
> SELECT R.Title FROM Recipes R
> WHERE (to_tsvector('english', title || description) @@
> plainto_tsquery('Cake'));
>
> and
>
> SELECT R.Title FROM Recipes R
> WHERE (to_tsvector('english', description || title) @@
> plainto_tsquery('Cake'));
>
>
> This query should search for the word 'Cake' in either the description OR the
> title field, correct?  The order should not matter.  However, in the first
> query I get 6 results and in the second I get 9.
>
> Furthermore, if I do:
>
> SELECT R.Title FROM Recipes R
> WHERE (to_tsvector('english', title) @@ plainto_tsquery('Cake'));
>
> I get 10 results and if I do:
>
> SELECT R.Title FROM Recipes R
> WHERE (to_tsvector('english', title || coalesce(description, '')) @@
> plainto_tsquery('Cake'));
>
> I get 7 results.  Shouldn't the first query result in a subset of the second
> query?  The first query returns several rows the second one doesn't return,
> and vice-versa!  This function is completely confusing me!!
>
> I would greatly appreciate anyone who could explain exactly how this works.
> It's most likely something stupid I'm doing that is the result of me not
> getting enough sleep..
>
> Mike
>
>

     Regards,
         Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83