PostgreSQL Python: Delete Data from Tables

Summary: This tutorial shows you how to delete data from PostgreSQL tables in Python.

This tutorial picks up from where the Querying Data from Tables Tutorial left off.

Steps for deleting data from a PostgreSQL table in Python

To delete data from the PostgreSQL table in Python, you use the following steps:

First, create a new database connection by calling the connect() function of the psycopg2 module.

conn = psycopg2.connect(config)

The connect() function returns a new connection object.

Next, create a new Cursor object by calling the cursor() method of the Connection object:

cur = conn.cursor()

Then, execute the DELETE statement. If you want to pass values to the DELETE statement, you use the placeholders ( %s) in the DELETE statement and pass input values to the second parameter of the execute() method.

The DELETE statement with a placeholder for the value of the id field is as follows:

DELETE FROM table_1 WHERE id = %s;

To bind value value1 to the placeholder, you call the execute() method and pass the input value as a tuple to the second parameter like the following:

cur.execute(delete_sql, (value1,))

After that, save the changes to the database permanently by calling the commit() method of the connection object.

conn.commit()

Finally, close the communication with the PostgreSQL database server by calling the close() method of the cursor and connection objects.

cur.close()
conn.close()

If you use context managers, you don’t need to explicitly close the cursor or connection.

Example of deleting data in PostgreSQL table in Python

We will use the parts table in the suppliers database for the demonstration purposes.

The following delete_part() function deletes a row in the parts table specified by the part_id.

import psycopg2
from config import load_config


def delete_part(part_id):
    """ Delete part by part id """

    rows_deleted  = 0
    sql = 'DELETE FROM parts WHERE part_id = %s'
    config = load_config()

    try:
        with  psycopg2.connect(**config) as conn:
            with  conn.cursor() as cur:
                # execute the UPDATE statement
                cur.execute(sql, (part_id,))
                rows_deleted = cur.rowcount

            # commit the changes to the database
            conn.commit()
    except (Exception, psycopg2.DatabaseError) as error:
        print(error)
    finally:
        return rows_deleted

if __name__ == '__main__':
    deleted_rows = delete_part(2)
    print('The number of deleted rows: ', deleted_rows)

Now we run the Python program to delete the part with the part id 1.

python delete.py

Output:

The number of deleted rows:  1

Retrieve data from the parts table again to confirm the deletion:

SELECT * FROM parts;

Output:

part_id |  part_name
---------+-------------
       1 | SIM Tray
       3 | Vibrator
       4 | Antenna
       5 | Home Button
       6 | LTE Modem
       8 | OLED
(6 rows)

The output indicates that part id 2 has been deleted successfully.

Download the project source code

Summary

• Use the execute() method of a cursor object to delete a row from a table.