if youre on 0.3, you can explicitly correlate to n1 by saying:
myselect.correlate(n1)
also in 0.3, it would probably help to say "scalar=True" in your
select() statement (and you dont need the alias):
n1 = node_table.alias('n1')
sub_query = select([func.max(node_table.c.id).label('max_id')],
(node_table.c.type_id==n1.c.type_id), scalar=True)
sub_query.correlate(n1)
n1.select(n1.c.id==sub_query.c.max_id).execute().fetchall()
if on 0.4, the whole thing is easier, id write it like this:
n1 = node_table.alias('n1')
sub_query = select([func.max(node_table.c.id).label('max_id')],
(node_table.c.type_id==n1.c.type_id)).as_scalar().correlate(n1)
n1.select(n1.c.id==sub_query.c.max_id).execute().fetchall()
however.....it *should* be correlating automatically anyway...some
combination of the "alias" and the no "scalar" might be affecting
that in the 0.3 version...what version are you using ?
On Aug 9, 2007, at 12:30 PM, Jeronimo wrote:
>
> Greetengs, i tried to solve the problem using different approaches but
> none of them worked.
> Here are the examples using both, plain SQL and SQLALchemy methods.
>
>
> * Using plain SQL:
>
> create table node(id integer, parent_id integer, type_id integer);
> insert into node(1,NULL,1);
> insert into node values(1,NULL,1);
> insert into node values(2,1,1);
> insert into node values(3,1,2);
> insert into node values(4,1,1);
>
> SELECT node.id, node.parent_id, node.type_id
> FROM node
> WHERE node.id = (SELECT max(n1.id) FROM node AS n1 WHERE n1.type_id =
> node.type_id);
>
>
> Results:
>
> id | parent_id | type_id
> ----+-----------+---------
> 3 | 1 | 2
> 4 | 1 | 1
> (2 rows)
>
>
>
> * Using SQLALchemy:
>
> class Node(BaseModel): pass
> node_table = Table('node', metadata, Column('id', Integer),
> Column('parent_id', Integer), Column('type_id', Integer))
> assign_mapper(session.context, Node, node_table)
>
> n1 = node_table.alias('n1')
> sub_query = select([func.max(node_table.c.id).label('max_id')],
> (node_table.c.type_id==n1.c.type_id)).alias('sub_query')
> n1.select(n1.c.id==sub_query.c.max_id).execute().fetchall()
>
>
> Results:
>
> [(4, 1, 1)]
>
>
> It seems that sub_query is not using the parent query field
> definitions, and instead is redeclaring node_table.
> Does someone knows whats happening ? Thanks in advance !
>
>
> Regards !
> Jeronimo
>
>
> >
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