I have a working query against postgresql that I was hoping to convert to 
Sequel. I've been using sql for more years than I can count, but this is my 
first use of a nested join. There may be another way to do it. But here is 
what I have, which returns the expected data:


SELECT a.*, b.info

FROM

api as a

left outer join (m_tuples as m inner join api as b on b.event_id=m.event_id 
and b.r_id=15) on a.m_id=m.m_id

where

a.r_id = 27


A simple representation of the tables should be:


api

event_id, m_id, r_id, info


m_tuples:

event_id, m_id


For the same m_id, there is at least a set of rows from api with r_id=27. 
There may also be a set of rows with r_id=15, so first it constructs a 
virtual table that ties m_tuples to api on event_id constrained to r_id 15, 
then left outer joins the api(a) to it. fwiw, api to m_tuples is a 
one-to-many for r_id 15, but unused for r_id 27.


I spent some time looking at the Dataset join methods and searching for 
ruby sequel nested joins, but came up empty handed. I noticed there was 
something about 'join_clause_sql_append', but I suspect that is not for 
this purpose and could find no example of it's use.


Many thanks,

Dan


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