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How to resolve SQLAlchemy Union Throwing Error

I'm using SQL Alchemy(Python, SQLServer) Union on two queries. It throws me the below error. Please help me in resolving it.
query1 = db.query(Employee.LastName).filter(Employee.Age == 30).all()
query2 = db.query(Employee.LastName).filter(Employee.Salary > 25000).all()
query3 = union(query1, query2).all()
**"SELECT construct for inclusion in UNION or other set construct expected, got [('Joseph',),('Alan',),('Joseph',)]."**
Also tried the below query and it throws the below error
query1 = db.query(Employee.LastName).filter(Employee.Age == 30).all()
query2 = db.query(Employee.LastName).filter(Employee.Salary > 25000).all()
query3 = query1.union(query2).all()
**"'list' object has no attribute 'union'"**

Remove the .all() from the first two queries, it turns the queries into lists, but you want to pass Query instances to union.
query1 = db.query(Employee.LastName).filter(Employee.Age == 30) # <- Query
query2 = db.query(Employee.LastName).filter(Employee.Salary > 25000) # <- Query
result = query1.union(query2).all() # <- List

Django Subquery, ORA-00904: invalid identifier

The query below works as raw sql
SELECT WORK_ORDER.*,(SELECT COMPLETE FROM SAMPLE WHERE COMPLETE = 'TRUE' AND
ARF_ID = WORK_ORDER.ARF_ID AND ROWNUM <= 1) AS SAMPLE_COMPLETE, (DUE_DATE -
SYSDATE) AS DUE_IN FROM WORK_ORDER WHERE COMPLETE = 'FALSE' ORDER BY
DUE_DATE ASC
The following Django Queryset does not work
subquery = Sample.objects.filter(complete = 'TRUE', arf_id = models.OuterRef('arf_id'))[:1]
workOrderList = WorkOrder.objects.annotate(sample_complete= models.Subquery(subquery.values('complete'))).annotate(due_in= models.F('due_date') - datetime.now()).filter(complete = 'FALSE').order_by('due_date')
which produces this query when running workOrderList.query
SELECT "WORK_ORDER"."ARF_ID", "WORK_ORDER"."COMPANY_NAME",
"WORK_ORDER"."COMPANY_ADDRESS", "WORK_ORDER"."CONTACT_TELEPHONE",
"WORK_ORDER"."ORDER_DATE", "WORK_ORDER"."DUE_DATE",
"WORK_ORDER"."ARF_NUMBER", "WORK_ORDER"."COMPLETE",
"WORK_ORDER"."COMPLETE_DATE", "WORK_ORDER"."REPORTED",
"WORK_ORDER"."REPORTED_DATE", "WORK_ORDER"."COMPANY_CODE", (SELECT * FROM
(SELECT "_SUB".* FROM (SELECT U0."COMPLETE" AS Col1 FROM "SAMPLE" U0 WHERE
(U0."COMPLETE" = TRUE AND U0."ARF_ID" = ("WORK_ORDER"."ARF_ID"))) "_SUB"
WHERE ROWNUM <= 1)) AS "SAMPLE_COMPLETE", ("WORK_ORDER"."DUE_DATE" - 2019-
01-28 13:00:51.043013) AS "DUE_IN" FROM "WORK_ORDER" WHERE
"WORK_ORDER"."COMPLETE" = FALSE ORDER BY "WORK_ORDER"."DUE_DATE" ASC
This returns error
cx_Oracle.DatabaseError: ORA-00904: "WORK_ORDER"."ARF_ID": invalid identifier
I am using Django 1.11.13 and this is a legacy database, I am comfortable using raw sql to query data but would like to learn/utilize the Django ORM the correct way so any fix or explanation why this won't work is helpful to me.

Using the Exists() subclass in this case works is a solution to accomplish the the overall goal:
workOrderList = WorkOrder.objects.annotate(sample_complete= models.Exists(subquery.values('complete')))
.annotate(due_in= models.F('due_date') - datetime.now()).filter(complete = 'FALSE').order_by('due_date')
I am still looking for a solution that uses the Subquery() method

Performing union with three queries - SQLAlchemy

In my project setup querying is being done based on the SQLAlchemy.
As per my previous requirements I have done the union with two queries.
Now I need to do Union with three queries.
Code is as follows:
query1 = query1.filter(model.name == "in-addr.arpa.")
query2 = query2.filter(model.tenant_id.in_(tenant_ids))
query = query1.union(query2)
Now Here I need to add one more query as follows:
query3 = query3.filter(model.tenant_id == context.tenant_id)
So I need to perform Union with all the three queries.

The solution is following:
query1 = query1.filter(model.name == "in-addr.arpa.")
query2 = query2.filter(model.tenant_id.in_(tenant_ids))
query3 = query3.filter(model.tenant_id == context.tenant_id)
query = query1.union(query2,query3)

This is how I did this in SQLAlchemy 1.3
from sqlalchemy import union
query1 = query1.filter(model.name == "in-addr.arpa.")
query2 = query2.filter(model.tenant_id.in_(tenant_ids))
query3 = query3.filter(model.tenant_id == context.tenant_id)
all_queries = [query1, query2, query3]
golden_set = union(*all_queries)
The change here is that the union method accepts a list of SQLAlchemy selectables.

In SQLAlchemy 1.4 you will need to use the function union and pass the queries as positional arguments instead of a list.
from sqlalchemy import union
query1 = query1.filter(model.name == "in-addr.arpa.")
query2 = query2.filter(model.tenant_id.in_(tenant_ids))
query3 = query3.filter(model.tenant_id == context.tenant_id)
query = union(query1, query2, query3)

SQLAlchemy Joining with subquery issue

I am trying to translate SQL into SQLAlchemy. The SQL version of the query I want is as follows:
SELECT * from calendarEventAttendee
JOIN calendarEventAttendanceActual ON calendarEventAttendanceActual.id = calendarEventAttendee.attendanceActualId
LEFT JOIN
(SELECT bill.id, bill.personId, billToEvent.eventId FROM bill JOIN billToEvent ON bill.id = billToEvent.billId) b
ON b.eventId = calendarEventAttendee.eventId AND b.personId = calendarEventAttendee.personId
WHERE b.id is NULL
My SQLAlchemy query is as follows:
query = db.session.query(CalendarEventAttendee).join(CalendarEventAttendanceActual)
sub_query = db.session.query(Bill, BillToEvent).join(BillToEvent, BillToEvent.billId == Bill.id).subquery()
query = query.outerjoin(sub_query, and_(sub_query.Bill.personId == CalendarEventAttendee.personId, Bill.eventId == CalendarEventAttendee.eventId))
results = query.all()
I am getting an error AttributeError: 'Alias' object has no attribute 'Bill'
If I adjust the SQLAlchemy query to the following:
sub_query = db.session.query(Bill, BillToEvent).join(BillToEvent, BillToEvent.billId == Bill.id).subquery()
query = query.outerjoin(sub_query, and_(sub_query.Bill.personId == CalendarEventAttendee.personId, sub_query.BillToEvent.eventId == CalendarEventAttendee.eventId))
results = query.all()
I get an error AttributeError: Bill
Any help would be appreciated, thanks!

Once you call subquery(), there is no access to objects, but only to columns via .c.{column_name} accessor.
Do the following for sub_query instead: load only the columns you need in order to avoid any name collisions:
sub_query = db.session.query(
Bill.id, Bill.personId, BillToEvent.eventId
).join(BillToEvent, BillToEvent.billId == Bill.id).subquery()
Then in your query use column names with .c.column_name:
query = query.outerjoin(
sub_query, and_(
sub_query.c.personId == CalendarEventAttendee.personId,
sub_query.c.eventId == CalendarEventAttendee.eventId)
)
results = query.all()

How can I get int result from web python sql query?

My code is as follows. My question is, how can I get the int result from the query?
import web
db = web.database(...)
rs = db.query('select max(id) from tablename')

The query method returns a list. Then you can access your calculated column by using an alias. If you don't want to use an alias, then I think you can do rs[0]['max(id)']
rs = db.query('select max(id) as max_value from tablename')
print rs[0].max_value
This is based on the example used in the web.py docs: http://webpy.org/cookbook/query
Here is the example from the link:
import web
db = web.database(dbn='postgres', db='mydata', user='dbuser', pw='')
results = db.query("SELECT COUNT(*) AS total_users FROM users")
print results[0].total_users # -> prints number of entries in 'users' table