SQLAlchemy中的别名联合查询

Question

在sqlalchemy中，我正在尝试合并表格，然后使用WHERE和ORDER_BY创建别名。

类似以下内容：

SELECT *
FROM (
  SELECT [TABLE_ONE].[SOME_ID] AS [SOME_ID]
  FROM [TABLE_ONE] 
  UNION 
  SELECT [TABLE_TWO].[SOME_ID] AS [SOME_ID]
  FROM [TABLE_TWO]
) AS anon_1
WHERE ...

SQLAlchemy:

select_q = select([TABLE_ONE.c.SOME_ID], TABLE_ONE)
select_w = select([TABLE_TWO.c.SOME_ID], TABLE_TWO)
union_qw = union(select_q,select_w) 
union_qw_aliased = aliased(union_qw)
s = select('*',union_qw_aliased)

但是SQLAlchemy生成的是SQL代码：

SELECT anon_1.[SOME_ID]
FROM (SELECT [TABLE_ONE].[SOME_ID] AS [SOME_ID]
FROM [TABLE_ONE] UNION SELECT [TABLE_TWO].[SOME_ID] AS [SOME_ID]
FROM [TABLE_TWO]) AS anon_1
WHERE SELECT [TABLE_ONE].[SOME_ID]
FROM [TABLE_ONE] UNION SELECT [TABLE_TWO].[SOME_ID]
FROM [TABLE_TWO]

非常感谢您的帮助。

- maxim

Answer 1

您正在错误使用“select()”的第二个参数，它实际上是“whereclause”（尽管我们现在鼓励使用where()方法）。FROM子句通常从您选择的列中隐含。对于您的“select *”，我们可以使用select_from()来设置显式FROM：

from sqlalchemy import *

m = MetaData()
t1 = Table('t1', m, Column('id', Integer))
t2 = Table('t2', m, Column('id', Integer))

select_q = select([t1])
select_w = select([t2])
union_qw = union(select_q, select_w)
union_qw_aliased = union_qw.alias()
s = select('*').select_from(union_qw_aliased)

print s

输出：

SELECT * 
FROM (SELECT t1.id AS id 
FROM t1 UNION SELECT t2.id AS id 
FROM t2) AS anon_1

如果需要执行更多的 WHERE 查询，可以使用 where() 来针对 union_qw_aliased 进行查询：

print s.where(union_qw_aliased.c.id == 5)

输出：

SELECT * 
FROM (SELECT t1.id AS id 
FROM t1 UNION SELECT t2.id AS id 
FROM t2) AS anon_1 
WHERE anon_1.id = :id_1

- zzzeek