Question

我尝试使用SQLAlchemy Core创建以下PostgreSQL查询：

SELECT DISTINCT ON (carrier) carrier,
       LAST_VALUE(ground) OVER wnd AS ground,
       LAST_VALUE(destinationzipstart) OVER wnd AS destinationzipstart,
       LAST_VALUE(destinationzipend) OVER wnd AS destionationzipend
FROM   tblshippingzone
WHERE  sourcezipstart <= 43234
AND    sourcezipend >= 43234
AND    destinationzipstart NOT BETWEEN 99500 AND 99950
AND    destinationzipstart NOT BETWEEN 96700 AND 96899
AND    destinationzipstart >= 1000
AND    (contiguous IS NULL OR contiguous = True)
AND    ground IS NOT NULL
WINDOW wnd AS (
   PARTITION BY carrier ORDER BY ground DESC, destinationzipstart);

这是我到目前为止所做的：

# Short-hand for accessing cols
all_cols = ShippingZoneDAL._table.c

# Window params
window_p = {'partition_by': all_cols.carrier,
            'order_by': [desc(all_cols.ground), all_cols.destination_zip_start]}

# Select columns
select_cols = [distinct(all_cols.carrier).label('carrier'),
           over(func.last_value(all_cols.ground), **window_p).label('ground'),
           over(func.last_value(all_cols.destination_zip_start), **window_p).label('destination_zip_start'),
           over(func.last_value(all_cols.destination_zip_end), **window_p).label('destination_zip_end')]

# Filter exprs
exprs = [all_cols.source_zip_start <= 43234,
     all_cols.source_zip_end >= 43234,
     ~all_cols.destination_zip_start.between(99500, 99950),  # Alaska zip codes
     ~all_cols.destination_zip_start.between(96700, 96899),  # Hawaii zip codes
     all_cols.destination_zip_start >= 1000,                 # Eliminates unusual territories
     or_(all_cols.contiguous == True, all_cols.contiguous == None),
     all_cols.ground != None]

# Build query
query = select(*select_cols).where(and_(*exprs))

但是在构建查询时出现错误：

ArgumentError: FROM expression expected

我在这里缺少什么想法？

奖励积分：

我最初希望窗口功能是这样的：

WINDOW wnd AS (
  PARTITION BY carrier ORDER BY ground
  ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING);

但根据这项支持请求，似乎sqlalchemy并不支持“无限制前进和无约束”之间的“行”： https://bitbucket.org/zzzeek/sqlalchemy/issue/3049/support-range-specificaiton-in-window

有没有办法使用该条款，还是没有？

Answer 1

这主要只是将各种方法重新安排到工作秩序中。如果有人碰到类似的东西，这就是答案：

# Short-hand for accessing cols
all_cols = ShippingZoneDAL._table.c

# Window params
window_p = {'partition_by': all_cols.carrier,
            'order_by': [desc(desc(all_cols.ground)), all_cols.destination_zip_start]}

# Select columns
select_cols = select(
                [all_cols.carrier,
                 func.last_value(all_cols.ground).over(**window_p).label(shipment_method),
                 func.last_value(all_cols.destination_zip_start).over(**window_p).label('destination_zip_start'),
                 func.last_value(all_cols.destination_zip_end).over(**window_p).label('destination_zip_end')])

# Filter exprs
exprs = [all_cols.source_zip_start <= 43234,
         all_cols.source_zip_end >= 43234,
         ~all_cols.destination_zip_start.between(99500, 99950),
         ~all_cols.destination_zip_start.between(96700, 96899),
         all_cols.destination_zip_start >= 1000,
         or_(all_cols.contiguous == True, all_cols.contiguous == None),
         all_cols.ground != None]

# Build query
query = select_cols.where(and_(*exprs)).distinct(all_cols.carrier)

使用上述解决方案时要记住的主要注意事项：

在此方案中，SQLAlchemy Core未见select(*select_cols)与select([all_cols.ground, etc])等效。可能是因为over方法需要在select的上下文中计算，否则你将丢失对FROM表的引用。
要使用PostgreSQL中的DISTINCT ON，请确保在主要选择之后 。如果仅在SELECT本身中使用，它将成为该列的标准DISTINCT子句。

请注意标签本身 - 返回的列只会定义key，而不会像对象的普通表列那样name。

如果有人还想解决我的奖励问题，请随意:)仍然不确定是否有一种方法可以在SQLAlchemy中使用它。

SQLAlchemy Core：为postgresql创建last_value窗口函数

1 个答案: