Q&A 4 How do you query data from a MySQL database?

4.1 Explanation

After setting up your database and inserting records, querying is how you extract useful information. The most common query is the SELECT statement, which lets you view specific data or filter based on conditions.

This Q&A demonstrates how to: - View all records - Filter data using WHERE - Sort data using ORDER BY

4.2 SQL/MySQL Code

-- Step 1: Switch into the CDI learning database
USE cdi_learning;

MariaDB [cdi_learning]> USE cdi_learning;
Database changed

-- Step 2: View all students
SELECT * FROM students;

MariaDB [cdi_learning]> SELECT * FROM students;
+----+---------------+-------------------+---------------+
| id | name          | email             | enrolled_date |
+----+---------------+-------------------+---------------+
|  1 | Alice Example | alice@example.com | 2025-08-10    |
|  2 | Bob Tester    | bob@test.com      | 2025-08-11    |
+----+---------------+-------------------+---------------+
2 rows in set (0.002 sec)

-- Step 3: View students enrolled after a given date (August 5, 2025)
SELECT * FROM students WHERE enrolled_date > '2025-08-05';

MariaDB [cdi_learning]> SELECT * FROM students WHERE enrolled_date > '2025-08-05';
+----+---------------+-------------------+---------------+
| id | name          | email             | enrolled_date |
+----+---------------+-------------------+---------------+
|  1 | Alice Example | alice@example.com | 2025-08-10    |
|  2 | Bob Tester    | bob@test.com      | 2025-08-11    |
+----+---------------+-------------------+---------------+
2 rows in set (0.004 sec)

-- Step 4: Sort students by enrollment date (most recent first)
SELECT * FROM students ORDER BY enrolled_date DESC;

MariaDB [cdi_learning]> SELECT * FROM students ORDER BY enrolled_date DESC;
+----+---------------+-------------------+---------------+
| id | name          | email             | enrolled_date |
+----+---------------+-------------------+---------------+
|  2 | Bob Tester    | bob@test.com      | 2025-08-11    |
|  1 | Alice Example | alice@example.com | 2025-08-10    |
+----+---------------+-------------------+---------------+
2 rows in set (0.004 sec)

4.3 Python Code (Querying MySQL via mysql-connector-python)

import mysql.connector

# Connect to MySQL
conn = mysql.connector.connect(
    host="localhost",
    user="root",
    password="",  # XAMPP default
    database="cdi_learning"
)

cursor = conn.cursor()

# Query 1: Get all students
cursor.execute("SELECT * FROM students")
print("All Students:")
for row in cursor.fetchall():
    print(row)

All Students:
(1, 'Alice Example', 'alice@example.com', datetime.date(2025, 8, 10))
(2, 'Bob Tester', 'bob@test.com', datetime.date(2025, 8, 11))


# Query 2: Filter by enrollment date
cursor.execute("SELECT * FROM students WHERE enrolled_date > %s", ("2025-08-05",))
print("\nFiltered Students:")
for row in cursor.fetchall():
    print(row)

conn.close()

Filtered Students:
(1, 'Alice Example', 'alice@example.com', datetime.date(2025, 8, 10))
(2, 'Bob Tester', 'bob@test.com', datetime.date(2025, 8, 11))

4.4 ✅ Learning Outcome

By the end of this Q&A, you will be able to:

Query data directly in SQL using SELECT
Filter rows with conditions using WHERE
Sort data using ORDER BY
Execute equivalent queries from Python with mysql-connector-python
Print and inspect query results inside Python

4.5 🧠 Takeaway

SQL is about asking the question; Python is about repeating it automatically.
Test queries in SQL first, then run them in Python to integrate results into scripts, apps, or data workflows.