On Monday, August 5, 2019 at 3:21:40 PM UTC-4, Michael wrote:
>
> Thanks a lot! Indeed SQLite seems to be the problem and the code works
> fine with PostgreSQL.
>
> Unfortunately, a full fledged database server is not an option. Therefore
> I probably have to work around the problem in Python.
>
> Is there an easy way to obtain a list of objects generated by multiple
> group_by conditions? Then I could calculate the percentiles e.g. in numpy.
>
If you can generate a function in raw sql that works with sqlite, you may
be able to use the @compiles to build a function in Python
as a very simple example, this is how i deal with sqlite wanting `least`
and postgres wanting `min`:
class min_date(expression.FunctionElement):
type = sqlalchemy.types.DateTime()
name = 'min_date'
@compiles(min_date)
def min_date__default(element, compiler, **kw):
# return compiler.visit_function(element)
"""
# just return the first date
"""
args = list(element.clauses)
return compiler.process(args[0])
@compiles(min_date, 'postgresql')
def min_date__postgresql(element, compiler, **kw):
"""
# select least(col_a, col_b);
"""
args = list(element.clauses)
return "LEAST(%s, %s)" % (
compiler.process(args[0]),
compiler.process(args[1]),
)
@compiles(min_date, 'sqlite')
def min_date__sqlite(element, compiler, **kw):
"""
# select min(col_a, col_b);
"""
args = list(element.clauses)
return "min(%s, %s)" % (
compiler.process(args[0]),
compiler.process(args[1]),
)
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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