python multiprocessing to download sql table

[Larz60+]

FYI: Possible alternative solution:

You might want to try pandas with sqlalchemy.
I have found this method to be very fast, and multiprocessing may not be necessary

The code is written as an example only, I don't expect that it will run without adding necessary schema, etc.
I have left notes where modifications are required.
The amount of code needed is very small.

It's easiest to create the ORM schema by first dumping your DBMS schema as a guide.
For example, In sqlite, this can be done from command line using sqlite3 as follows:

$ sqlite3
sqlite> .schema AD # your tablename here

with output similar to:

Output:
CREATE TABLE IF NOT EXISTS "AD" (
	"RecordType" VARCHAR NOT NULL, 
	"UniqueSystemIdentifier" VARCHAR NOT NULL, 
	"ULSFileNumber" VARCHAR, 
	"EBF_Number" VARCHAR, 
	"ApplicationPurpose" VARCHAR, 
	"ApplicationStatus" VARCHAR, 
	"ApplicationFeeExempt" VARCHAR, 
	"RegulatoryFeeExempt" VARCHAR, 

Other DBMS will have similar utility.

Note: Code below will not run without modification
Example code:

from pathlib import Path
import pandas as pd
from sqlalchemy.ext.declarative import declarative_base
# you can add or remove datatypes from import as needed
from sqlalchemy import (Column, String, Integer, Date, create_engine,
    DateTime, ForeignKey)

# replace actual path to database, and DBMS type in engine statement below
engine = create_engine(f"sqlite:///{path_to_database}")
Base = declarative_base()

# You will need to replace schema below eith actual schema for UK_Table
# keep lines 14 and 16 
# I added the following as an example only
class UK_Table(Base):

    __tablename__ = 'UK_Table'

    # --------------------------------------------------------
    # create schema here -- replace example with your schema
    # Following is only an example schema
    # --------------------------------------------------------

    RecordType = Column(String, primary_key=True, nullable=False)
    UniqueSystemIdentifier = Column(String, primary_key=True, nullable=False)
    ULSFileNumber = Column(String, nullable=True)
    EBF_Number = Column(String, index=True, nullable=True)
    ApplicationPurpose = Column(String, index=True, nullable=True)
    ApplicationStatus = Column(String, index=True, nullable=True)
    ApplicationFeeExempt = Column(String, nullable=True)
    RegulatoryFeeExempt = Column(String, nullable=True)


class CsvFromSQL:
    def __init__(self):
        self.csvfile = Path("E:\\backup\\output.csv")
    
    def save_table_to_csv:
        df = read_sql(__tablename__, con=self.UK_Table.engine)
        # Note: see https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.to_csv.html
        # for csv write options.
        df.to_csv(self.cavfile)


def main():
    cfs = CsvFromSQL()
    cfs.save_table_to_csv()


if __name__ == '__main__':
    main()