> Merge Join (cost=111885.70..319492.88 rows=13016048 width=620)
The outermost merge join has to go through 13 million rows. If you
remove "distinct on (bien.uid)", you'll see that.
> LEFT outer JOIN ville ON ville.uid = bien.ref_ville
> LEFT outer JOIN freguesia_ville ON freguesia_ville.ref_ville =ville.uid
This is not enough. You have to add this condition as well:
AND bien.ref_ville = freguesia_ville.ref_ville
In other words, when you link three tables by a common field, all three
relationships should be explicitly expressed, otherwise you'll have this
type of explosive row multiplication.
Although I don't quite understand the purpose of the query, I don't
think you need all those OUTER joins.
Regards,
Mike