Slow performance with left outer join

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Hi,
 
Since I moved from PostgreSQL 7.3 to 8.2 I have a query which suddenly runs very slow. In 7.3 it was really fast. It seems that the query analyser makes other choices, which I don't understand.
 
I have the query:
 
SELECT * FROM fpuArticle
    LEFT OUTER JOIN fpuArticleText ON a_No=at_a_No AND coalesce(at_Type,1)=1 AND coalesce(at_Language,0)=0
    WHERE strpos(lower(coalesce(a_Code,'') || ' ' || coalesce(at_Text,'')), 'string')>0
 
when I use a normal join, this query is very fast, but with this left outer join it is slow.
 
This is the query analysis:
 
Nested Loop Left Join  (cost=1796.69..3327.98 rows=5587 width=516)
  Join Filter: (fpuarticle.a_no = fpuarticletext.at_a_no)
  Filter: (strpos(lower((((COALESCE(fpuarticle.a_code, ''::character varying))::text || ' '::text) || (COALESCE(fpuarticletext.at_text, ''::character varying))::text)), 'string'::text) > 0)
  ->  Seq Scan on fpuarticle  (cost=0.00..944.62 rows=16762 width=386)
  ->  Materialize  (cost=1796.69..1796.70 rows=1 width=130)
        ->  Seq Scan on fpuarticletext  (cost=0.00..1796.69 rows=1 width=130)
              Filter: ((COALESCE((at_type)::integer, 1) = 1) AND (COALESCE(at_language, 0::numeric) = 0::numeric))
 
It seems that the filter on at_type and at_Language is used at the and, while it is much faster to use it at the beginning. Why is this, and how can I influence this?
 
With kind regards
 
Marten Verhoeven
Van Beek B.V.

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