Create new table from query results is slow in Python with SQLite

Using Python, I try to create a new SQLite table in a database from a query result which is executed on two other tables in that database.

For the record, the query is

CREATE TABLE results AS

    SELECT table_1.*, table_2.*
    FROM table_1
        LEFT JOIN table_2
            ON table_1.ID_1 = table_2.ID_2
    UNION ALL
    SELECT table_1.*, table_2.*
    FROM table_2
        LEFT JOIN table_1
            ON table_1.ID_1 = table_2.ID_2
    WHERE table_1.ID_1 IS NULL

which is supposed to be a workaround for a FULL OUTER JOIN which is not directly available in SQLite (this method can be found on different SO threads on this topic).

However, this operation is slow on my tables with ~1 million rows each... so slow that I get the impression it's going to take hours when hitting refresh in the Explorer Window showing the database's file size while updating.

How can I get this faster? I already did a lot of research on this and most of the time, people are talking about using transactions because otherwise, each row will open up a new connection to the database or whatever... however, I could not find a working example on how to use this.

My two approaches so far which are way too slow:

Using Python's sqlite3 module:

# open sqlite database
conn = sqlite3.connect('Database.sqlite')

# get a cursor
cursor = conn.cursor()

# start query
cursor.execute("""
CREATE TABLE results AS
    SELECT allShapesMerged.*, allDbfsMerged.*
    FROM allShapesMerged
        LEFT JOIN allDbfsMerged
            ON allShapesMerged.ID = allDbfsMerged.NETWORK_ID
    UNION ALL
    SELECT allShapesMerged.*, allDbfsMerged.*
    FROM allDbfsMerged
        LEFT JOIN allShapesMerged
            ON allShapesMerged.ID = allDbfsMerged.NETWORK_ID
    WHERE allShapesMerged.ID IS NULL
;""")

Using sqalchemy:

from sqlalchemy import create_engine, event
from sqlite3 import dbapi2 as sqlite

# create database engine
engine = create_engine('sqlite:///Database.sqlite')

# open sqlite database
connection = engine.connect()

# query
with connection.begin() as trans:
    connection.execute("BEGIN TRANSACTION;")

    connection.execute("""
    CREATE TABLE results AS

        SELECT allShapesMerged.*, allDbfsMerged.*
        FROM allShapesMerged
            LEFT JOIN allDbfsMerged
                ON allShapesMerged.ID = allDbfsMerged.NETWORK_ID
        UNION ALL
        SELECT allShapesMerged.*, allDbfsMerged.*
        FROM allDbfsMerged
            LEFT JOIN allShapesMerged
                ON allShapesMerged.ID = allDbfsMerged.NETWORK_ID
        WHERE allShapesMerged.ID IS NULL
    ;""")

    trans.commit()