Python MySQL Join

Last modified on: October 19, 2024

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<h3><strong>Using JOINs in MySQL with Python</strong></h3>
<p>JOINs are used in SQL to combine rows from two or more tables based on a related column between them. This guide will show you how to use JOINs in MySQL with Python.</p>
<hr />
<h3><strong>1. Prerequisites</strong></h3>
<p>Ensure you have:</p>
<ul>
<li>MySQL installed and running.</li>
<li>The <code>mysql-connector-python</code> library installed. If you haven't done this yet, run:</li>
</ul>
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<pre class="language-python"><code>pip install mysql-connector-python
</code></pre>
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<h3><strong>2. Import Required Libraries</strong></h3>
<p>Start by importing the necessary libraries in your Python script:</p>
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<pre class="language-python"><code>import mysql.connector
from mysql.connector import Error
</code></pre>
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<h3><strong>3. Establish a Connection to MySQL</strong></h3>
<p>Connect to your MySQL database as shown below:</p>
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<pre class="language-python"><code>def create_connection(host_name, user_name, user_password, db_name):
    connection = None
    try:
        connection = mysql.connector.connect(
            host=host_name,
            user=user_name,
            password=user_password,
            database=db_name
        )
        print("Connection to MySQL DB successful")
    except Error as e:
        print(f"The error '{e}' occurred")
    return connection
</code></pre>
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<h3><strong>4. Using JOINs to Query Data</strong></h3>
<p>Create a function to perform a JOIN query. Here&rsquo;s an example that uses an <code>INNER JOIN</code> to combine data from two tables: <code>users</code> and <code>orders</code>.</p>
<h4>Example Tables:</h4>
<ul>
<li>
<p><strong>users</strong>:</p>
<ul>
<li>id (INT)</li>
<li>name (VARCHAR)</li>
</ul>
</li>
<li>
<p><strong>orders</strong>:</p>
<ul>
<li>id (INT)</li>
<li>user_id (INT)</li>
<li>product (VARCHAR)</li>
</ul>
</li>
</ul>
<h4>Querying with INNER JOIN</h4>
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<pre class="language-python"><code>def fetch_user_orders(connection):
    join_query = """
    SELECT users.name, orders.product
    FROM users
    INNER JOIN orders ON users.id = orders.user_id;
    """
    cursor = connection.cursor()
    try:
        cursor.execute(join_query)
        results = cursor.fetchall()
        for row in results:
            print(f"User: {row[0]}, Product: {row[1]}")
    except Error as e:
        print(f"The error '{e}' occurred")
</code></pre>
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<h3><strong>5. Putting It All Together</strong></h3>
<p>Here&rsquo;s a complete example that connects to the MySQL database and fetches user orders:</p>
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<pre class="language-python"><code># Import the necessary libraries
import mysql.connector
from mysql.connector import Error

# Function to create a connection
def create_connection(host_name, user_name, user_password, db_name):
    connection = None
    try:
        connection = mysql.connector.connect(
            host=host_name,
            user=user_name,
            password=user_password,
            database=db_name
        )
        print("Connection to MySQL DB successful")
    except Error as e:
        print(f"The error '{e}' occurred")
    return connection

# Function to fetch user orders using INNER JOIN
def fetch_user_orders(connection):
    join_query = """
    SELECT users.name, orders.product
    FROM users
    INNER JOIN orders ON users.id = orders.user_id;
    """
    cursor = connection.cursor()
    try:
        cursor.execute(join_query)
        results = cursor.fetchall()
        for row in results:
            print(f"User: {row[0]}, Product: {row[1]}")
    except Error as e:
        print(f"The error '{e}' occurred")

# Main logic
if __name__ == "__main__":
    # Establish a connection to the MySQL server
    connection = create_connection("localhost", "your_username", "your_password", "my_database")
    
    # Fetch and print user orders
    fetch_user_orders(connection)

# Close the connection
    if connection.is_connected():
        connection.close()
        print("Connection closed")
</code></pre>
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<h3><strong>6. Running the Script</strong></h3>
<ol>
<li>Replace <code>your_username</code>, <code>your_password</code>, and <code>my_database</code> with your actual MySQL username, password, and database name.</li>
<li>Ensure that the <code>users</code> and <code>orders</code> tables exist with appropriate data.</li>
<li>Run the script. If successful, it will retrieve and print the names of users along with their ordered products.</li>
</ol>
<h3><strong>Conclusion</strong></h3>
<p>In this tutorial, you learned how to:</p>
<ul>
<li>Connect to a MySQL database using Python.</li>
<li>Use <code>INNER JOIN</code> to combine data from multiple tables.</li>
</ul>
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