Why Aren't My Python MySQL Updates Reflecting in the Database?

Troubleshooting MySQL and Python Database Update Issues

When attempting to update data in a MySQL database using Python, developers may encounter situations where changes made through Python code do not reflect in the database when queried directly. This article investigates this issue and provides a potential solution.

Problem Description

As described by a user, a program using MySQLdb to update a database row fails to save the changes persistently. The code executes an update query but, upon inspecting the database via the command line interface (CLI), the updates are not observed.

import MySQLdb

conn = MySQLdb.connect(host="localhost", user="root", passwd="pass", db="dbname")
cursor = conn.cursor()

cursor.execute("UPDATE compinfo SET Co_num=4 WHERE ID=100")
cursor.execute("SELECT Co_num FROM compinfo WHERE ID=100")
results = cursor.fetchall()

for row in results:
    print row[0]

print "Number of rows updated: %d" % cursor.rowcount

cursor.close()
conn.close()

Solution

The issue stems from the default transaction handling in MySQLdb. By default, MySQLdb disables autocommit, meaning changes made to the database are not persisted until a commit operation is explicitly executed. To resolve the problem, the code should include a call to conn.commit() before closing the connection:

import MySQLdb

conn = MySQLdb.connect(host="localhost", user="root", passwd="pass", db="dbname")
cursor = conn.cursor()

cursor.execute("UPDATE compinfo SET Co_num=4 WHERE ID=100")
# Commit the changes to the database
conn.commit()

cursor.execute("SELECT Co_num FROM compinfo WHERE ID=100")
results = cursor.fetchall()

for row in results:
    print row[0]

print "Number of rows updated: %d" % cursor.rowcount

cursor.close()
conn.close()

With conn.commit(), the changes are committed to the database, ensuring that subsequent queries reflect the updated values.

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