Question

I need execute 2 select in SQLAlchemy. For example:

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

The problem is that. I don’t know how to write “” value in select2 with SQLAlchemy.

Thanks.

Answer 1

You probably want some combination of column, literal_column or null, which are in the sqlalchemy.sql module:

>>> 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
>>>