Re: 2 left joins causes seqscan

The equivalent of your first query is to take the result sets from
these two queries:

select a1.field1, b1.title, b2.title
  from a a1
  join b b1 on b1.id = a1.id and b1.lang = 1
  left join b b2 on (b2.id = a1.id and b2.lang = 2)
  where lower(b1.title) like'abcd%'
union
select a2.field1, b4.title, b3.title
  from a a2
  join b b3 on b3.id = a2.id and b3.lang = 2
  left join b b4 on (b4.id = a2.id and b4.lang = 1)
  where lower(b3.title) like'abcd%';