SQL and Python work best together when responsibilities are clear.
SQLite engine behavior is documented in the official documentation SQLite Consortium (2026).
query = '''
SELECT c.full_name,
SUM(oi.quantity * oi.unit_price) AS revenue
FROM customers c
JOIN orders o ON c.customer_id = o.customer_id
JOIN order_items oi ON o.order_id = oi.order_id
GROUP BY c.full_name
ORDER BY revenue DESC;
'''
df = pd.read_sql(query, con)
print(df) full_name revenue
0 Joseph Kimaro 25.75
1 Amina Hassan 19.50
2 Grace Nyerere 17.80
3 Neema Msuya 2.50plt.bar(df["full_name"], df["revenue"])
plt.xticks(rotation=45)
plt.title("Revenue by Customer")
plt.tight_layout()
plt.show()
A common workflow mistake is to load full tables into Python and then join or filter there.
Better practice is to:
This keeps analysis efficient and reduces opportunities for structural mistakes.