python - SQLAlchemy Writing Nested Query -

i have 2 tables:

table  id | values 

and

table b  id | foreign key | datestamp | val2 

given list of ids a, how joined result of a , b rows b have earliest datestamp each matched a.

for example table b have:

1 | 2 | 1/10/2015 1 | 2 | 1/2/2015 1 | 2 | 1/3/2015 

i interested in row

id_a | id_b | 1/2/2015 | values | val2 

to understanding in sql, can like

where timestamp = (select min(timestamp) b.x x.id = b.id) 

however, how nest select inside sqlalchemy query?

for example, believe can't use

.filter(b.timestamp == (query(func.min(b.timestamp)).filter(a.id == b.foreign_key_to_a))) 

actually, can use:

b2 = aliased(b, name='b2') s = session.query(func.min(b2.datestamp)).filter(b2.a_id == a.id) q = (session      .query(a.id, b.id, b.datestamp, a.values, b.val2)      .join(b)      .filter(b.datestamp == s)      )