具有不同列數的SQLAlchemy聯盟

Question

我需要在SQLAlchemy中執行2選擇。例如：

select1 = Session.query(col1, col2, col3, col4).filter(...) 
select2 = Session.query(col1, "", "", col4).filter(...) 
result = select1.union(select2).all() 

問題是這樣的。我不知道如何使用SQLAlchemy在select2中編寫「」值。

謝謝。

Answer 1

你可能想的column，literal_column或null，這是sqlalchemy.sql模塊中的一些組合：

>>> print Query((t.c.col1, 
...    t.c.col2, 
...    t.c.col3, 
...    t.c.col4)) \ 
... .union(
...  Query((t.c.col1, 
...    sqlalchemy.sql.null().label('c2'), 
...    sqlalchemy.sql.literal_column('""').label('c3'), 
...    t.c.col2)) 
...  ) 
SELECT anon_1.table_col1 AS anon_1_table_col1, anon_1.table_col2 AS anon_1_table_col2, anon_1.table_col3 AS anon_1_table_col3, anon_1.table_col4 AS anon_1_table_col4 
FROM (SELECT "table".col1 AS table_col1, "table".col2 AS table_col2, "table".col3 AS table_col3, "table".col4 AS table_col4 
FROM "table" UNION SELECT "table".col1 AS table_col1, NULL AS c2, "" AS c3, "table".col2 AS table_col2 
FROM "table") AS anon_1 
>>>