基于此处找到的示例,但我想我不理解它。这适用于单列主键,但在多个主键上失败。这是我的代码
@classmethod
def column_windows(cls, q, columns, windowsize, where = None):
"""Return a series of WHERE clauses against
a given column that break it into windows.
Result is an iterable of tuples, consisting of
((start, end), whereclause), where (start, end) are the ids.
Requires a database that supports window functions,
i.e. Postgresql, SQL Server, Oracle.
Enhance this yourself ! Add a "where" argument
so that windows of just a subset of rows can
be computed.
"""
#Here is the thing... how to compare...
def int_for_range(start_id, end_id):
if end_id:
return and_(
columns>=start_id,
columns<end_id
)
else:
return columns>=start_id
if isinstance(columns, Column):
columns_k=(columns,)
else:
columns_k=tuple(columns)
q2=None
cols=()
for c in columns:
cols = cols + (c,)
if not q2:
q2=q.session.query(c)
else:
q2=q2.add_column(c)
q2 = q2.add_column(func.row_number().over(order_by=columns_k).label('rownum'))
q2=q2.filter(q._criterion).from_self(cols)
if windowsize > 1:
q2 = q2.filter("rownum %% %d=1" % windowsize)
for res in q2:
print res
intervals = [id for id, in q2]
while intervals:
start = intervals.pop(0)
if intervals:
end = intervals[0]
else:
end = None
yield int_for_range(start, end)
@classmethod
def windowed_query(cls, q, columns, windowsize):
""""Break a Query into windows on a given column."""
for whereclause in cls.column_windows(q,columns, windowsize):
for row in q.filter(whereclause).order_by(columns):
yield row
现在我在比较主键的列集时遇到了问题。好吧,我猜应该是一种递归子句生成函数……让我们试试吧……