Re: [Sqlalchemy-tickets] [sqlalchemy] #2746: Add a flag to explicitly enable correlation even when the subquery has `asfrom=True`

[sqlalchemy <mi...@zz...>]

#2746: Add a flag to explicitly enable correlation even when the subquery has
`asfrom=True`
------------------------------+----------------------------------
      Reporter:  sayap        |      Owner:  zzzeek
          Type:  enhancement  |     Status:  new
      Priority:  highest      |  Milestone:  0.8.xx
     Component:  sql          |   Severity:  minor - half an hour
    Resolution:               |   Keywords:
Progress State:  needs tests  |
------------------------------+----------------------------------

Comment (by zzzeek):

 from that change we also can fix correlate_except, which also doesn't do
 the right thing here:

 {{{
 #!python
 from sqlalchemy.sql import table, column, select, exists

 t1 = table('t1', column('x'))
 t2 = table('t2', column('y'))
 t3 = table('t3', column('z'))

 s = select([t1]).where(t1.c.x == t2.c.y).where(t2.c.y ==
 t3.c.z).correlate_except(t1)

 print s
 }}}

 we want:

 {{{
 SELECT t1.x
 FROM t1, t2, t3
 WHERE t1.x = t2.y AND t2.y = t3.z
 }}}

 and not

 {{{
 SELECT t1.x
 FROM t1
 WHERE t1.x = t2.y AND t2.y = t3.z
 }}}

 a similar pattern to the latter is called "backwards correlated" in
 test_compiler...but its wrong, and I'd like to be able to add other FROM
 clauses to an `any()` or `has()`.

 This is getting pretty changy.  I don't think there's a real-world use for
 "backwards correlated" and correlate_except() is fairly new so hopefully
 this is safe for 0.8 still.

--
Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2746#comment:5>
sqlalchemy <http://www.sqlalchemy.org/>
The Database Toolkit for Python