[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:  task   |          Status:  new
 Priority:  low    |       Milestone:
Component:  sql    |        Severity:  no triage selected yet
 Keywords:         |  Progress State:  not decided upon
-------------------+-----------------------------------------
 This is related to the mailing list post:
 https://groups.google.com/forum/?fromgroups#!topic/sqlalchemy/Ld0iuCUphHU

 It seems like #2668 has universally disabled correlation for subquery
 inside a FROM clause. The situations where such expression is needed could
 be quite rare, but it is sometimes necessary to do so, especially for
 lesser databases such as SQL Server. An example would be this:

 http://stackoverflow.com/questions/5786739/porting-postgresql-string-agg-
 to-sql-server-problem-with-order-by

 Another example would be a subquery that returns a couple of computed
 values, with an outer query consists entirely of a CASE statement in its
 select list that makes use of the values.

 (Note that these examples are used in the context of hybrid / column
 property)

 I think it would be good to add a flag to `select()` to enforce the
 correlation when necessary.

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