Re: [sqlalchemy] Mapping a CTE
I am interested in any feedback on the code at https://gist.github.com/1156683 . The code works for me but it's a hacked solution and I'm not sure if this will work generally. I am not sure if there is a better way to handle gather the CTE's, I simply tacked the found CTE onto the compiler object. Also this should support multiple CTE's. print Date.range('2011-01-01 00:00:00', '2012-02-01 00:00:00').filter(date='2011-01-15 00:00:00').order_by(Date.date.desc()) WITH all_dates(date) AS ( SELECT CAST(? AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, ?, date) AS [DATEADD_1] FROM all_dates WHERE DATEADD(dd, ?, date) = CAST(? AS DATETIME) ) SELECT date AS date FROM (SELECT * FROM all_dates) as x WHERE date='2011-01-15 00:00:00' ORDER BY date DESC OPTION (MAXRECURSION 0) On Thu, Aug 18, 2011 at 2:20 PM, Michael Bayer mike...@zzzcomputing.comwrote: On Aug 18, 2011, at 2:01 PM, Marc DellaVolpe wrote: I understand what you are saying about this being an uphill battle on mssql. If we ignore the CTE for the moment and pretend that all_dates is a regular table, shouldn't there be no difference for generation. You can subquery as needed and all that really needs to happen is to prepend the CTE to the rest of the SQL before execution. Maybe this approach isn't generally applicable, CTE's already make my head hurt :) yeah that could work as well but its not clear to me if the CTE can be up above everything, then referenced within a nested structure like that.I haven't really worked with CTEs to have that level of experience. Searching the mailing list found a thread ( http://groups.google.com/group/sqlalchemy/browse_thread/thread/c20a4f380e277af/fb179a515bf48868) where you used a regular expression to shim in a special comment. This seems hackish but could a similar approach work on mssql? Is it possible to hook into only the top-level/last Select's compile()? if it works, then yes you'd get your Select compiler to dig in, look for CTEs, put the WITH all the way on top, assuming the Select is the outermost. You can tell if you're the outermost select by checking bool(compiler.stack), which is a stack of SELECT constructs. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Mapping a CTE
I found the following CTE demo (http://www.sqlalchemy.org/trac/ attachment/ticket/1859/cte_demo.py) and I was wondering if there was any way to map these selects. I have built a CTE based select to generate a dates table on the fly and I would love to be able to map this and use generative selects to transform queries. I have only been able to make the mapping work with .from_statement() however this does not allow for transformations. Any thoughts? Thanks, -Marc with CommonTableExpression.create('all_dates', ['date']) as all_dates: start_exp = cast(bindparam('start'), DateTime) end_exp = cast(bindparam('stop'), DateTime) exp = func.DATEADD( literal_column('dd'), bindparam('step'), all_dates.c.date ) s1 = select([start_exp]) s2 = select([exp], from_obj=all_dates).where(exp = end_exp) s = s1.union_all(s2) all_dates = SelectFromCTE(all_dates, s) class Date(object): query = Session.query_property() @classmethod def range(cls, start, stop, step=1): return cls.query.from_statement(str(all_dates)).params(start=start, stop=stop, step=step) mapper(Date, all_dates, primary_key=[all_dates.c.date]) print Date.range('2011-01-01 00:00:00', '2021-01-01 00:00:00').all() -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] Mapping a CTE
On Aug 18, 2011, at 11:23 AM, Marc DellaVolpe wrote: I found the following CTE demo (http://www.sqlalchemy.org/trac/ attachment/ticket/1859/cte_demo.py) and I was wondering if there was any way to map these selects. I have built a CTE based select to generate a dates table on the fly and I would love to be able to map this and use generative selects to transform queries. I have only been able to make the mapping work with .from_statement() however this does not allow for transformations. Any thoughts? Thanks, -Marc with CommonTableExpression.create('all_dates', ['date']) as all_dates: start_exp = cast(bindparam('start'), DateTime) end_exp = cast(bindparam('stop'), DateTime) exp = func.DATEADD( literal_column('dd'), bindparam('step'), all_dates.c.date ) s1 = select([start_exp]) s2 = select([exp], from_obj=all_dates).where(exp = end_exp) s = s1.union_all(s2) all_dates = SelectFromCTE(all_dates, s) class Date(object): query = Session.query_property() @classmethod def range(cls, start, stop, step=1): return cls.query.from_statement(str(all_dates)).params(start=start, stop=stop, step=step) mapper(Date, all_dates, primary_key=[all_dates.c.date]) print Date.range('2011-01-01 00:00:00', '2021-01-01 00:00:00').all() this maps fine for me (it's best to apply alias() to all_dates before mapping), I just get a statement that doesn't work: SELECT anon_1.date AS anon_1_date FROM (WITH RECURSIVE all_dates(date) AS (SELECT CAST(%(start)s AS TIMESTAMP WITHOUT TIME ZONE) AS anon_2 UNION ALL SELECT DATEADD(dd, %(step)s, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, %(step)s, all_dates.date) = CAST(%(stop)s AS TIMESTAMP WITHOUT TIME ZONE)) SELECT * FROM all_dates) AS anon_1 (ProgrammingError) column dd does not exist what should dd be here ? -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] Mapping a CTE
I should have mentioned, I modified the CTE demo to work on SQL Server and I believe (I will double check this...) that on SQL Server the with of the CTE needs to be at the top of the statement and referenced in subqueries below. The generated SQL SELECT FROM (WITH ...) is invalid on SQL Server. The goal is to render SQL similar to: WITH all_dates(date) AS ( SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, date) = CAST(:stop AS DATETIME) ) SELECT * FROM all_dates OPTION (MAXRECURSION 0) In order for this to work on SQL Server as a mapped class I believe it would need to be rendered similar to: WITH RECURSIVE all_dates(date) AS (SELECT CAST(%(start)s AS TIMESTAMP WITHOUT TIME ZONE) AS anon_2 UNION ALL SELECT DATEADD(dd, %(step)s, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, %(step)s, all_dates.date) = CAST(%(stop)s AS TIMESTAMP WITHOUT TIME ZONE)) SELECT anon_1.date AS anon_1_date FROM (SELECT * FROM all_dates) AS anon_1 -Marc On Thu, Aug 18, 2011 at 11:47 AM, Michael Bayer mike...@zzzcomputing.comwrote: On Aug 18, 2011, at 11:23 AM, Marc DellaVolpe wrote: I found the following CTE demo (http://www.sqlalchemy.org/trac/ attachment/ticket/1859/cte_demo.py) and I was wondering if there was any way to map these selects. I have built a CTE based select to generate a dates table on the fly and I would love to be able to map this and use generative selects to transform queries. I have only been able to make the mapping work with .from_statement() however this does not allow for transformations. Any thoughts? Thanks, -Marc with CommonTableExpression.create('all_dates', ['date']) as all_dates: start_exp = cast(bindparam('start'), DateTime) end_exp = cast(bindparam('stop'), DateTime) exp = func.DATEADD( literal_column('dd'), bindparam('step'), all_dates.c.date ) s1 = select([start_exp]) s2 = select([exp], from_obj=all_dates).where(exp = end_exp) s = s1.union_all(s2) all_dates = SelectFromCTE(all_dates, s) class Date(object): query = Session.query_property() @classmethod def range(cls, start, stop, step=1): return cls.query.from_statement(str(all_dates)).params(start=start, stop=stop, step=step) mapper(Date, all_dates, primary_key=[all_dates.c.date]) print Date.range('2011-01-01 00:00:00', '2021-01-01 00:00:00').all() this maps fine for me (it's best to apply alias() to all_dates before mapping), I just get a statement that doesn't work: SELECT anon_1.date AS anon_1_date FROM (WITH RECURSIVE all_dates(date) AS (SELECT CAST(%(start)s AS TIMESTAMP WITHOUT TIME ZONE) AS anon_2 UNION ALL SELECT DATEADD(dd, %(step)s, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, %(step)s, all_dates.date) = CAST(%(stop)s AS TIMESTAMP WITHOUT TIME ZONE)) SELECT * FROM all_dates) AS anon_1 (ProgrammingError) column dd does not exist what should dd be here ? -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] Mapping a CTE
On Aug 18, 2011, at 11:56 AM, Marc DellaVolpe wrote: I should have mentioned, I modified the CTE demo to work on SQL Server and I believe (I will double check this...) that on SQL Server the with of the CTE needs to be at the top of the statement and referenced in subqueries below. The generated SQL SELECT FROM (WITH ...) is invalid on SQL Server. Just to confirm, the WITH RECURSIVE can never be nested inside of any kind of subquery with SQL Server (which would not be surprising given SQL Servers standard MO), is that correct ? That blows away a large amount of generations right there with Query since subqueries are a core part of its operation. As the ticket states, the CTE logic would probably need to be inside of the compilation of Select itself. The mapper itself only knows how to select columns from a selectable given, such as a table or other SELECT statement. So if SELECT myexpr.date FROM (WITH RECURSIVE) is impossible, either you have to stick to using your from_statement() approach, or you'd need to modify the compilation of Select() such that it generates *nothing* if the thing being selected from is a CTE, which is quite awkward, surprising, and I can't see us ever having it do that by default, but here's that: from sqlalchemy.sql.expression import Select @compiles(Select) def _dont_render_outside_of_cte(element, compiler, **kw): if element._froms: expr = element._froms[0] else: expr = None if isinstance(expr, SelectFromCTE): return compiler.process(expr, **kw) else: return compiler.visit_select(element, **kw) the mapping + query: class Date(Base): __table__ = all_dates __mapper_args__ = {'primary_key':(all_dates.c.date)} @classmethod def range(cls, start, stop, step=1): return Session().query(Date).params(start=start, stop=stop, step=step) Session = scoped_session(sessionmaker()) print Date.range('2011-01-01 00:00:00', '2021-01-01 00:00:00') produces: WITH RECURSIVE all_dates(date) AS SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, all_dates.date) = CAST(:stop AS DATETIME) SELECT * FROM all_dates The goal is to render SQL similar to: WITH all_dates(date) AS ( SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, date) = CAST(:stop AS DATETIME) ) SELECT * FROM all_dates OPTION (MAXRECURSION 0) In order for this to work on SQL Server as a mapped class I believe it would need to be rendered similar to: WITH RECURSIVE all_dates(date) AS (SELECT CAST(%(start)s AS TIMESTAMP WITHOUT TIME ZONE) AS anon_2 UNION ALL SELECT DATEADD(dd, %(step)s, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, %(step)s, all_dates.date) = CAST(%(stop)s AS TIMESTAMP WITHOUT TIME ZONE)) SELECT anon_1.date AS anon_1_date FROM (SELECT * FROM all_dates) AS anon_1 -Marc On Thu, Aug 18, 2011 at 11:47 AM, Michael Bayer mike...@zzzcomputing.com wrote: On Aug 18, 2011, at 11:23 AM, Marc DellaVolpe wrote: I found the following CTE demo (http://www.sqlalchemy.org/trac/ attachment/ticket/1859/cte_demo.py) and I was wondering if there was any way to map these selects. I have built a CTE based select to generate a dates table on the fly and I would love to be able to map this and use generative selects to transform queries. I have only been able to make the mapping work with .from_statement() however this does not allow for transformations. Any thoughts? Thanks, -Marc with CommonTableExpression.create('all_dates', ['date']) as all_dates: start_exp = cast(bindparam('start'), DateTime) end_exp = cast(bindparam('stop'), DateTime) exp = func.DATEADD( literal_column('dd'), bindparam('step'), all_dates.c.date ) s1 = select([start_exp]) s2 = select([exp], from_obj=all_dates).where(exp = end_exp) s = s1.union_all(s2) all_dates = SelectFromCTE(all_dates, s) class Date(object): query = Session.query_property() @classmethod def range(cls, start, stop, step=1): return cls.query.from_statement(str(all_dates)).params(start=start, stop=stop, step=step) mapper(Date, all_dates, primary_key=[all_dates.c.date]) print Date.range('2011-01-01 00:00:00', '2021-01-01 00:00:00').all() this maps fine for me (it's best to apply alias() to all_dates before mapping), I just get a statement that doesn't work: SELECT anon_1.date AS anon_1_date FROM (WITH RECURSIVE all_dates(date) AS (SELECT CAST(%(start)s AS TIMESTAMP WITHOUT TIME ZONE) AS anon_2 UNION ALL SELECT DATEADD(dd, %(step)s, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, %(step)s, all_dates.date) = CAST(%(stop)s AS TIMESTAMP WITHOUT TIME ZONE)) SELECT * FROM
Re: [sqlalchemy] Mapping a CTE
From what I can tell from http://msdn.microsoft.com/en-us/library/ms190766.aspx and experimentally, you can only put CTE's at the top: -- Works WITH all_dates(date) AS ( SELECT CAST('2011-01-01' AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, 1, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, 1, date) = CAST('2012-01-01' AS DATETIME) ) select * from (SELECT * FROM all_dates) as x OPTION (MAXRECURSION 0) -- Generates an invalid syntax error select * from ( WITH all_dates(date) AS ( SELECT CAST('2011-01-01' AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, 1, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, 1, date) = CAST('2012-01-01' AS DATETIME) ) ) as x OPTION (MAXRECURSION 0) Thank you for the solution. One approach I was considering was subclassing Select, adding a method to attach a CTE to the select and then generating custom SQL for the subclass but I wasn't completely familiar of the compilation workings to determine if this was workable solution to force the CTE to the top of the generated SQL. -Marc On Thu, Aug 18, 2011 at 12:13 PM, Michael Bayer mike...@zzzcomputing.comwrote: On Aug 18, 2011, at 11:56 AM, Marc DellaVolpe wrote: I should have mentioned, I modified the CTE demo to work on SQL Server and I believe (I will double check this...) that on SQL Server the with of the CTE needs to be at the top of the statement and referenced in subqueries below. The generated SQL SELECT FROM (WITH ...) is invalid on SQL Server. Just to confirm, the WITH RECURSIVE can never be nested inside of any kind of subquery with SQL Server (which would not be surprising given SQL Servers standard MO), is that correct ? That blows away a large amount of generations right there with Query since subqueries are a core part of its operation. As the ticket states, the CTE logic would probably need to be inside of the compilation of Select itself. The mapper itself only knows how to select columns from a selectable given, such as a table or other SELECT statement. So if SELECT myexpr.date FROM (WITH RECURSIVE) is impossible, either you have to stick to using your from_statement() approach, or you'd need to modify the compilation of Select() such that it generates *nothing* if the thing being selected from is a CTE, which is quite awkward, surprising, and I can't see us ever having it do that by default, but here's that: from sqlalchemy.sql.expression import Select @compiles(Select) def _dont_render_outside_of_cte(element, compiler, **kw): if element._froms: expr = element._froms[0] else: expr = None if isinstance(expr, SelectFromCTE): return compiler.process(expr, **kw) else: return compiler.visit_select(element, **kw) the mapping + query: class Date(Base): __table__ = all_dates __mapper_args__ = {'primary_key':(all_dates.c.date)} @classmethod def range(cls, start, stop, step=1): return Session().query(Date).params(start=start, stop=stop, step=step) Session = scoped_session(sessionmaker()) print Date.range('2011-01-01 00:00:00', '2021-01-01 00:00:00') produces: WITH RECURSIVE all_dates(date) AS SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, all_dates.date) = CAST(:stop AS DATETIME) SELECT * FROM all_dates The goal is to render SQL similar to: WITH all_dates(date) AS ( SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, date) = CAST(:stop AS DATETIME) ) SELECT * FROM all_dates OPTION (MAXRECURSION 0) In order for this to work on SQL Server as a mapped class I believe it would need to be rendered similar to: WITH RECURSIVE all_dates(date) AS (SELECT CAST(%(start)s AS TIMESTAMP WITHOUT TIME ZONE) AS anon_2 UNION ALL SELECT DATEADD(dd, %(step)s, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, %(step)s, all_dates.date) = CAST(%(stop)s AS TIMESTAMP WITHOUT TIME ZONE)) SELECT anon_1.date AS anon_1_date FROM (SELECT * FROM all_dates) AS anon_1 -Marc On Thu, Aug 18, 2011 at 11:47 AM, Michael Bayer mike...@zzzcomputing.comwrote: On Aug 18, 2011, at 11:23 AM, Marc DellaVolpe wrote: I found the following CTE demo (http://www.sqlalchemy.org/trac/ attachment/ticket/1859/cte_demo.py) and I was wondering if there was any way to map these selects. I have built a CTE based select to generate a dates table on the fly and I would love to be able to map this and use generative selects to transform queries. I have only been able to make the mapping work with .from_statement() however this does not allow for transformations. Any thoughts? Thanks, -Marc with CommonTableExpression.create('all_dates', ['date']) as all_dates: start_exp = cast(bindparam('start'), DateTime)
Re: [sqlalchemy] Mapping a CTE
There seems to be a problem with the custom compilation. print Session.query(Date).order_by(Date.date.desc()) WITH all_dates(date) AS ( SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, date) = CAST(:stop AS DATETIME) ) SELECT * FROM all_dates OPTION (MAXRECURSION 0) On Thu, Aug 18, 2011 at 1:08 PM, Marc DellaVolpe marc.dellavo...@gmail.comwrote: From what I can tell from http://msdn.microsoft.com/en-us/library/ms190766.aspx and experimentally, you can only put CTE's at the top: -- Works WITH all_dates(date) AS ( SELECT CAST('2011-01-01' AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, 1, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, 1, date) = CAST('2012-01-01' AS DATETIME) ) select * from (SELECT * FROM all_dates) as x OPTION (MAXRECURSION 0) -- Generates an invalid syntax error select * from ( WITH all_dates(date) AS ( SELECT CAST('2011-01-01' AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, 1, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, 1, date) = CAST('2012-01-01' AS DATETIME) ) ) as x OPTION (MAXRECURSION 0) Thank you for the solution. One approach I was considering was subclassing Select, adding a method to attach a CTE to the select and then generating custom SQL for the subclass but I wasn't completely familiar of the compilation workings to determine if this was workable solution to force the CTE to the top of the generated SQL. -Marc On Thu, Aug 18, 2011 at 12:13 PM, Michael Bayer mike...@zzzcomputing.comwrote: On Aug 18, 2011, at 11:56 AM, Marc DellaVolpe wrote: I should have mentioned, I modified the CTE demo to work on SQL Server and I believe (I will double check this...) that on SQL Server the with of the CTE needs to be at the top of the statement and referenced in subqueries below. The generated SQL SELECT FROM (WITH ...) is invalid on SQL Server. Just to confirm, the WITH RECURSIVE can never be nested inside of any kind of subquery with SQL Server (which would not be surprising given SQL Servers standard MO), is that correct ? That blows away a large amount of generations right there with Query since subqueries are a core part of its operation. As the ticket states, the CTE logic would probably need to be inside of the compilation of Select itself. The mapper itself only knows how to select columns from a selectable given, such as a table or other SELECT statement. So if SELECT myexpr.date FROM (WITH RECURSIVE) is impossible, either you have to stick to using your from_statement() approach, or you'd need to modify the compilation of Select() such that it generates *nothing* if the thing being selected from is a CTE, which is quite awkward, surprising, and I can't see us ever having it do that by default, but here's that: from sqlalchemy.sql.expression import Select @compiles(Select) def _dont_render_outside_of_cte(element, compiler, **kw): if element._froms: expr = element._froms[0] else: expr = None if isinstance(expr, SelectFromCTE): return compiler.process(expr, **kw) else: return compiler.visit_select(element, **kw) the mapping + query: class Date(Base): __table__ = all_dates __mapper_args__ = {'primary_key':(all_dates.c.date)} @classmethod def range(cls, start, stop, step=1): return Session().query(Date).params(start=start, stop=stop, step=step) Session = scoped_session(sessionmaker()) print Date.range('2011-01-01 00:00:00', '2021-01-01 00:00:00') produces: WITH RECURSIVE all_dates(date) AS SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, all_dates.date) = CAST(:stop AS DATETIME) SELECT * FROM all_dates The goal is to render SQL similar to: WITH all_dates(date) AS ( SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, date) = CAST(:stop AS DATETIME) ) SELECT * FROM all_dates OPTION (MAXRECURSION 0) In order for this to work on SQL Server as a mapped class I believe it would need to be rendered similar to: WITH RECURSIVE all_dates(date) AS (SELECT CAST(%(start)s AS TIMESTAMP WITHOUT TIME ZONE) AS anon_2 UNION ALL SELECT DATEADD(dd, %(step)s, all_dates.date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, %(step)s, all_dates.date) = CAST(%(stop)s AS TIMESTAMP WITHOUT TIME ZONE)) SELECT anon_1.date AS anon_1_date FROM (SELECT * FROM all_dates) AS anon_1 -Marc On Thu, Aug 18, 2011 at 11:47 AM, Michael Bayer mike...@zzzcomputing.com wrote: On Aug 18, 2011, at 11:23 AM, Marc DellaVolpe wrote: I found the following CTE demo (http://www.sqlalchemy.org/trac/ attachment/ticket/1859/cte_demo.py) and I was wondering if there was any way to map these
Re: [sqlalchemy] Mapping a CTE
On Aug 18, 2011, at 1:28 PM, Marc DellaVolpe wrote: There seems to be a problem with the custom compilation. print Session.query(Date).order_by(Date.date.desc()) WITH all_dates(date) AS ( SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, date) = CAST(:stop AS DATETIME) ) SELECT * FROM all_dates OPTION (MAXRECURSION 0) Heh. This is what I was saying - Query is going to produce SELECT x, y, z FROM (your custom statement) ORDER BY order by.You blow away that SELECT on the outside you lose the ORDER BY also and anything else.The only path here would involve a much more concerted effort with the overriding of the Select construct to pull off everything it does and apply it to the thing that's being wrapped.Each new thing you'd like to do, like JOIN to it, etc., means your magic compiler would need to work it out. The key issue here is that SQL Server doesn't supply a generically useful form of CTE since it cannot be nested. Very uphill. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] Mapping a CTE
I understand what you are saying about this being an uphill battle on mssql. If we ignore the CTE for the moment and pretend that all_dates is a regular table, shouldn't there be no difference for generation. You can subquery as needed and all that really needs to happen is to prepend the CTE to the rest of the SQL before execution. Maybe this approach isn't generally applicable, CTE's already make my head hurt :) Searching the mailing list found a thread ( http://groups.google.com/group/sqlalchemy/browse_thread/thread/c20a4f380e277af/fb179a515bf48868) where you used a regular expression to shim in a special comment. This seems hackish but could a similar approach work on mssql? Is it possible to hook into only the top-level/last Select's compile()? Thanks for all of your help. -Marc On Thu, Aug 18, 2011 at 1:37 PM, Michael Bayer mike...@zzzcomputing.comwrote: On Aug 18, 2011, at 1:28 PM, Marc DellaVolpe wrote: There seems to be a problem with the custom compilation. print Session.query(Date).order_by(Date.date.desc()) WITH all_dates(date) AS ( SELECT CAST(:start AS DATETIME) AS anon_1 UNION ALL SELECT DATEADD(dd, :step, date) AS DATEADD_1 FROM all_dates WHERE DATEADD(dd, :step, date) = CAST(:stop AS DATETIME) ) SELECT * FROM all_dates OPTION (MAXRECURSION 0) Heh. This is what I was saying - Query is going to produce SELECT x, y, z FROM (your custom statement) ORDER BY order by.You blow away that SELECT on the outside you lose the ORDER BY also and anything else.The only path here would involve a much more concerted effort with the overriding of the Select construct to pull off everything it does and apply it to the thing that's being wrapped.Each new thing you'd like to do, like JOIN to it, etc., means your magic compiler would need to work it out. The key issue here is that SQL Server doesn't supply a generically useful form of CTE since it cannot be nested. Very uphill. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.