Musterlösung mit Erklärung

import csv
import os

import psycopg
from psycopg.rows import dict_row

SCHEMA = '''
CREATE TABLE IF NOT EXISTS verkaeufe (
    id SERIAL PRIMARY KEY,
    kunde TEXT NOT NULL,
    artikel TEXT NOT NULL,
    menge INT NOT NULL,
    preis NUMERIC(10, 2) NOT NULL
)
'''


def lese_csv(pfad):
    with open(pfad, newline='', encoding='utf-8-sig') as f:
        return [
            (z['kunde'], z['artikel'], int(z['menge']), z['preis'])
            for z in csv.DictReader(f, delimiter=';')
        ]


def main():
    zeilen = lese_csv('verkaeufe.csv')

    with psycopg.connect(os.environ['DATABASE_URL'], row_factory=dict_row) as conn:
        conn.execute(SCHEMA)
        with conn.cursor() as cur:
            cur.executemany(
                'INSERT INTO verkaeufe (kunde, artikel, menge, preis) VALUES (%s, %s, %s, %s)',
                zeilen,
            )
        auswertung = conn.execute('''
            SELECT kunde, SUM(menge * preis) AS umsatz
            FROM verkaeufe
            GROUP BY kunde
            ORDER BY umsatz DESC
        ''').fetchall()

    print(f'{len(zeilen)} Zeilen importiert')
    for z in auswertung:
        print(f'{z["kunde"]:<10}{z["umsatz"]:>10.2f}')


if __name__ == '__main__':
    main()