I have two tables beard
and moustache
defined below:
x
+--------+---------+------------+-------------+
| person | beardID | beardStyle | beardLength |
+--------+---------+------------+-------------+
+--------+-------------+----------------+
| person | moustacheID | moustacheStyle |
+--------+-------------+----------------+
I have created a SQL Query in PostgreSQL which will combine these two tables and generate following result:
+--------+---------+------------+-------------+-------------+----------------+
| person | beardID | beardStyle | beardLength | moustacheID | moustacheStyle |
+--------+---------+------------+-------------+-------------+----------------+
| bob | 1 | rasputin | 1 | | |
+--------+---------+------------+-------------+-------------+----------------+
| bob | 2 | samson | 12 | | |
+--------+---------+------------+-------------+-------------+----------------+
| bob | | | | 1 | fu manchu |
+--------+---------+------------+-------------+-------------+----------------+
Query:
SELECT * FROM beards LEFT OUTER JOIN mustaches ON (false) WHERE person = "bob"
UNION ALL
SELECT * FROM beards b RIGHT OUTER JOIN mustaches ON (false) WHERE person = "bob"
However I can not create SQLAlchemy representation of it. I tried several ways from implementing from_statement
to outerjoin
but none of them really worked. Can anyone help me with it?
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Answer
From @Francis P‘s suggestion I came up with this snippet:
q1 = session.
query(beard.person.label('person'),
beard.beardID.label('beardID'),
beard.beardStyle.label('beardStyle'),
sqlalchemy.sql.null().label('moustachID'),
sqlalchemy.sql.null().label('moustachStyle'),
).
filter(beard.person == 'bob')
q2 = session.
query(moustache.person.label('person'),
sqlalchemy.sql.null().label('beardID'),
sqlalchemy.sql.null().label('beardStyle'),
moustache.moustachID,
moustache.moustachStyle,
).
filter(moustache.person == 'bob')
result = q1.union(q2).all()
However this works but you can’t call it as an answer because it appears as a hack. This is one more reason why there should be RIGHT OUTER JOIN
in sqlalchemy.