Python 在SQLAlchemy中截断小时/天/周/月/年
在适用于所有DBMS(尤其是Postgres和SQLite)的SQLAlchemy中,是否有一种方法可以将datetime截断为小时/天/周/月/年?不是现成的,但是您可以制作一个(我想这与): Postgresql的编译器很简单:Python 在SQLAlchemy中截断小时/天/周/月/年,python,sql,sqlalchemy,Python,Sql,Sqlalchemy,在适用于所有DBMS(尤其是Postgres和SQLite)的SQLAlchemy中,是否有一种方法可以将datetime截断为小时/天/周/月/年?不是现成的,但是您可以制作一个(我想这与): Postgresql的编译器很简单: @compiles(Trunc, 'postgresql') def compile_trunc_postgresql(element, compiler, **kw): return compiler.process(func.date_trunc(ele
@compiles(Trunc, 'postgresql')
def compile_trunc_postgresql(element, compiler, **kw):
return compiler.process(func.date_trunc(element.precision, element.expr))
SQLite版本更复杂,因为没有一个停止的截断解决方案:
_modifiers = {
'year': ('start of year',),
'month': ('start of month',),
# This does not account for locale specific first day of week. 1 day
# is added so that the 1st day of week won't truncate to previous week.
# Replace 'weekday 0' with 'weekday 1', if you'd like first day of
# week to be Monday (in accordance with ISO 8601)
'week': ('1 day', 'weekday 0', '-7 days', 'start of day'),
'day': ('start of day',),
}
@compiles(Trunc, 'sqlite')
def compile_trunc_sqlite(element, compiler, **kw):
precision = element.precision
expr = element.expr
modifiers = _modifiers.get(precision)
if modifiers:
return compiler.process(func.datetime(expr, *modifiers))
elif precision == 'hour':
return compiler.process(func.datetime(
expr,
func.strftime('-%M minutes', expr),
func.strftime('-%f seconds', expr)))
elif precision == 'minute':
return compiler.process(func.datetime(
expr, func.strftime('-%f seconds', expr)))
elif precision == 'second':
return compiler.process(func.datetime(
expr,
func.strftime('-%f seconds', expr),
func.strftime('%S seconds', expr)))
SQLite版本不支持Postgresql中可用的所有精度修饰符,如“quarter”,但应该非常有用。用法:
In [16]: for p in ['year', 'month', 'week', 'day', 'hour', 'minute', 'second']:
...: print(engine.execute(select([Trunc(p, func.current_timestamp())])).scalar())
...:
2018-01-01 00:00:00
2018-08-01 00:00:00
2018-07-29 00:00:00
2018-08-03 00:00:00
2018-08-03 06:00:00
2018-08-03 06:18:00
2018-08-03 06:18:18
不是现成的,但您可以制作一个(我想这与): Postgresql的编译器很简单:
@compiles(Trunc, 'postgresql')
def compile_trunc_postgresql(element, compiler, **kw):
return compiler.process(func.date_trunc(element.precision, element.expr))
SQLite版本更复杂,因为没有一站式的截断解决方案:
_modifiers = {
'year': ('start of year',),
'month': ('start of month',),
# This does not account for locale specific first day of week. 1 day
# is added so that the 1st day of week won't truncate to previous week.
# Replace 'weekday 0' with 'weekday 1', if you'd like first day of
# week to be Monday (in accordance with ISO 8601)
'week': ('1 day', 'weekday 0', '-7 days', 'start of day'),
'day': ('start of day',),
}
@compiles(Trunc, 'sqlite')
def compile_trunc_sqlite(element, compiler, **kw):
precision = element.precision
expr = element.expr
modifiers = _modifiers.get(precision)
if modifiers:
return compiler.process(func.datetime(expr, *modifiers))
elif precision == 'hour':
return compiler.process(func.datetime(
expr,
func.strftime('-%M minutes', expr),
func.strftime('-%f seconds', expr)))
elif precision == 'minute':
return compiler.process(func.datetime(
expr, func.strftime('-%f seconds', expr)))
elif precision == 'second':
return compiler.process(func.datetime(
expr,
func.strftime('-%f seconds', expr),
func.strftime('%S seconds', expr)))
SQLite版本不支持Postgresql中可用的所有精度修饰符,如“quarter”,但应该非常有用。用法:
In [16]: for p in ['year', 'month', 'week', 'day', 'hour', 'minute', 'second']:
...: print(engine.execute(select([Trunc(p, func.current_timestamp())])).scalar())
...:
2018-01-01 00:00:00
2018-08-01 00:00:00
2018-07-29 00:00:00
2018-08-03 00:00:00
2018-08-03 06:00:00
2018-08-03 06:18:00
2018-08-03 06:18:18
我还有一个问题。使用Trunc类的查询不会转换为
子查询
。你知道我该如何修复它吗?是的,匆忙地编写并使用了错误的基类。应该是ColumnElement
。我还有一个问题。使用Trunc类的查询不会转换为子查询
。你知道我该如何修复它吗?是的,匆忙地编写并使用了错误的基类。应该是ColumnElement
。