Unexpected results when joining two subqueries with SQLAlchemy - sqlalchemy

Question

I have a large SQL table as follows,
Id Firstname Lastname tran_id insert_datetime
==============================================================
1 Tom Smith 0 2020-08-07 15:37:32
2 Tom Smith 0 2020-08-06 06:33:44
3 Tom Smith 1 2020-08-07 12:43:53
4 Foo Bar 7 2020-08-24 23:43:21
5 Foo Bar 0 2020-08-25 14:23:24
....
and I'm trying to group it by (firstname, lastname, date) and obtain the number of transactions except those with tran_id = 0 as follows:
Firstname Lastname date num_tran
==============================================================
Tom Smith 2020-08-25 0
Tom Smith 2020-08-26 2
Foo Bar 2020-08-25 1
Foo Bar 2020-08-26 0
....
I was able to achieve this in MySQL by doing the following:
SELECT a.firstname, a.lastname, a.date,
CASE
WHEN b.num_tran IS NOT NULL THEN b.num_tran
ELSE 0
END AS num_tran
FROM
(SELECT firstname, lastname, DATE(insert_datetime) AS date
FROM table
WHERE a.insert_datetime >= '2020-08-25' AND a.insert_datetime <= ' 2020-08-27'
GROUP BY firstname, lastname, date
) a
LEFT OUTER JOIN
(SELECT firstname, lastname, DATE(insert_datetime) AS date, COUNT(Id) AS num_tran
FROM table
WHERE tran_id != 0 AND a.insert_datetime >= '2020-08-25' AND a.insert_datetime <= ' 2020-08-27'
GROUP BY firstname, lastname, date
) b
ON a.firstname = b.firstname, a.lastname = b.lastname, a.date = b.date
I tried to transform this to SQLAlchemy as shown below:
from sqlalchemy import func, case, cast, Date
from sqlalchemy.sql import label
# First full table subquery
full_table = (
request.dbsession.query(
table.firstname,
table.lastname,
label('date', cast(table.insert_datetime, Date))
)
.filter(
table.insert_datetime >= '2020-08-25',
table_insert_datetime <= '2020-08-27')
.group_by(
table.firstname,
table.lastname,
cast(table.insert_datetime, Date))
.subquery()
)
# Second subquery
num_transactions = (
request.dbsession.query(
table.firstname,
table.lastname,
label('date', cast(table.insert_datetime, Date)
label('num_tran', func.count(table.id))
)
.filter(
table.tran_id != 0,
table.insert_datetime >= '2020-08-25',
table.insert_datetime <= '2020-08-27')
.group_by(
table.firstname,
table.lastname,
cast(table.insert_datetime, Date))
.subquery()
)
# Left outer join to get final table
result_table = (
request.dbsession.query(
full_table.c.firstname,
full_table.c.lastname,
full_table.c.date,
case(
[(num_transactions.c.num_tran == None, 0)],
else_=num_transaction.c.num_tran)
.label('num_tran'))
.join(num_transactions,
(full_table.c.firstname == num_transaction.c.firstname) &
(full_table.c.lastname == num_transaction.c.lastname) &
(full_table.c.date == num_transaction.c.date),
isouter=True)
)
However, I get tens of thousands of results and it obviously does not match the results of the query in MySQL. Is there somewhere I'm going wrong in how I'm writing the query using SQLAlchemy?