Python MySQL Tutorial – How to DELETE Data from a Table

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Tags:- MySQL Python

When working with MySQL databases in Python, deleting records is just as important as inserting or selecting them. In this tutorial, you’ll learn how to safely delete data from a MySQL table using Python and the mysql-connector-python library.


Table of Contents

  1. What is the DELETE Statement?

  2. Prerequisites

  3. Install MySQL Connector

  4. Connect to MySQL Database

  5. DELETE with WHERE Clause

  6. DELETE Multiple Records

  7. Preventing Accidental Deletes

  8. Full Working Example

  9. Tips and Common Pitfalls


✅ 1. What is the DELETE Statement?

The DELETE statement in SQL is used to remove one or more records from a table.

Basic SQL Syntax:

DELETE FROM table_name WHERE condition;

⚠️ Always use a WHERE clause unless you intend to delete all records.


⚙️ 2. Prerequisites

Make sure you have the following:

  • Python installed

  • A running MySQL Server

  • A MySQL database with a table and data

  • The mysql-connector-python library installed


3. Install MySQL Connector

Install the required MySQL library:

pip install mysql-connector-python

4. Connect to MySQL Database

import mysql.connector

db = mysql.connector.connect(
    host="localhost",
    user="your_username",
    password="your_password",
    database="mydatabase"
)

cursor = db.cursor()

Replace your_username, your_password, and mydatabase with your actual credentials.


5. DELETE with WHERE Clause

The safest way to delete data is by specifying a condition:

sql = "DELETE FROM users WHERE id = %s"
val = (3,)

cursor.execute(sql, val)
db.commit()

print(cursor.rowcount, "record(s) deleted")

Explanation:

  • %s is a placeholder to prevent SQL injection

  • val is a tuple with the value to match

  • .commit() is necessary to apply changes to the database


6. DELETE Multiple Records

You can delete multiple records by expanding your condition:

sql = "DELETE FROM users WHERE age < %s"
val = (18,)

cursor.execute(sql, val)
db.commit()

print(cursor.rowcount, "record(s) deleted")

This removes all users under the age of 18.


7. Preventing Accidental Deletes

NEVER run a DELETE statement without a WHERE clause unless you’re intentionally clearing a table.

❌ Dangerous:

cursor.execute("DELETE FROM users")

✅ Safer:

sql = "DELETE FROM users WHERE email = %s"
val = ("[email protected]",)

8. Full Working Example

import mysql.connector
from mysql.connector import Error

def delete_user(user_id):
    try:
        db = mysql.connector.connect(
            host="localhost",
            user="root",
            password="your_password",
            database="mydatabase"
        )

        cursor = db.cursor()

        sql = "DELETE FROM users WHERE id = %s"
        val = (user_id,)
        cursor.execute(sql, val)
        db.commit()

        print(f"{cursor.rowcount} record(s) deleted")

    except Error as e:
        print("Error:", e)

    finally:
        if db.is_connected():
            db.close()
            print("Database connection closed.")

# Example usage
delete_user(5)

⚠️ 9. Tips and Common Pitfalls

Issue Solution
Forgot db.commit() No changes will be saved
Using DELETE without WHERE All rows will be deleted
Wrong condition in WHERE clause No rows will be deleted
Placeholder error Ensure tuple structure is correct ((val,))

✅ Best Practices

  • Always use parameterized queries to avoid SQL injection.

  • Double-check your WHERE clause before executing.

  • Use .rowcount to confirm how many rows were deleted.

  • Perform backups before destructive operations.


Summary Table

Task Code
Delete one record DELETE FROM users WHERE id = %s
Delete by condition DELETE FROM users WHERE age < %s
Commit changes db.commit()
Check rows deleted cursor.rowcount

Final Thoughts

Using the DELETE statement in Python with MySQL is powerful but should be handled with care. Always ensure your queries are specific, safe, and use parameterization. With good practices, deleting data becomes a reliable part of managing your applications.

 

Tips and Tricks


What is pass in Python?

Python | Pass Statement

The pass statement is used as a placeholder for future code. It represents a null operation in Python. It is generally used for the purpose of filling up empty blocks of code which may execute during runtime but has yet to be written.

 

def myfunction():
    pass

 


How can you generate random numbers?

Python | Generate random numbers

Python provides a module called random using which we can generate random numbers. e.g: print(random.random())

 

 

We have to import a random module and call the random() method as shown below:

 import random

 print(random.random())

The random() method generates float values lying between 0 and 1 randomly.


To generate customized random numbers between specified ranges, we can use the randrange() method
Syntax: randrange(beginning, end, step)
 

import random

print(random.randrange(5,100,2))

 


What is lambda in Python?

Python | Lambda function

A lambda function is a small anonymous function. This function can have any number of parameters but, can have just one statement.
 

 

Syntex: 
lambda arguments : expression
 

a = lambda x,y : x+y

print(a(5, 6))

It also provides a nice way to write closures. With that power, you can do things like this.

def adder(x):
    return lambda y: x + y

add5 = adder(5)

add5(1)    #6

As you can see from the snippet of Python, the function adder takes in an argument x and returns an anonymous function, or lambda, that takes another argument y. That anonymous function allows you to create functions from functions. This is a simple example, but it should convey the power lambdas and closures have.
 


What is swapcase() function in the Python?

Python | swapcase() Function

It is a string's function that converts all uppercase characters into lowercase and vice versa. It automatically ignores all the non-alphabetic characters.
 

string = "IT IS IN LOWERCASE."  

print(string.swapcase())  

 


How to remove whitespaces from a string in Python?

Python | strip() Function | Remove whitespaces from a string 

To remove the whitespaces and trailing spaces from the string, Python provides a strip([str]) built-in function. This function returns a copy of the string after removing whitespaces if present. Otherwise returns the original string.
 

string = "  Python " 
 
print(string.strip())  

 


What is the usage of enumerate() function in Python?

Python | enumerate() Function

The enumerate() function is used to iterate through the sequence and retrieve the index position and its corresponding value at the same time.
 

lst = ["A","B","C"] 
 
print (list(enumerate(lst)))

#[(0, 'A'), (1, 'B'), (2, 'C')]

 


Can you explain the filter(), map(), and reduce() functions?

Python | filter(), map(), and reduce() Functions

  • filter()  function accepts two arguments, a function and an iterable, where each element of the iterable is filtered through the function to test if the item is accepted or not.
    >>> set(filter(lambda x:x>4, range(7)))
    
    # {5, 6}
    
    

     

  • map() function calls the specified function for each item of an iterable and returns a list of result

    >>> set(map(lambda x:x**3, range(7)))
    
    # {0, 1, 64, 8, 216, 27, 125}

     

  • reduce() function reduces a sequence pair-wise, repeatedly until we arrive at a single value..
     

    >>> reduce(lambda x,y:y-x, [1,2,3,4,5])
    
    # 3
    

    Let’s understand this:

    2-1=1
    3-1=2
    4-2=2
    5-2=3

    Hence, 3.

 


What is a namedtuple?

Python | namedtuple

A namedtuple will let us access a tuple’s elements using a name/label. We use the function namedtuple() for this, and import it from collections.

>>> from collections import namedtuple

#format
>>> result=namedtuple('result','Physics Chemistry Maths') 

#declaring the tuple
>>> Chris=result(Physics=86,Chemistry=92,Maths=80) 

>>> Chris.Chemistry
# 92

 


Write a code to add the values of same keys in two different dictionaries and return a new dictionary.

We can use the Counter method from the collections module

from collections import Counter

dict1 = {'a': 5, 'b': 3, 'c': 2}
dict2 = {'a': 2, 'b': 4, 'c': 3}

new_dict = Counter(dict1) + Counter(dict2)


print(new_dict)
# Print: Counter({'a': 7, 'b': 7, 'c': 5})


 


Python In-place swapping of two numbers

 Python | In-place swapping of two numbers

>>> a, b = 10, 20
>>> print(a, b)
10 20

>>> a, b = b, a
>>> print(a, b)
20 10

 


Reversing a String in Python

Python | Reversing a String

>>> x = 'PythonWorld'
>>> print(x[: : -1])
dlroWnohtyP

 


Python join all items of a list to convert into a single string

Python | Join all items of a list to convert into a single string

>>> x = ["Python", "Online", "Training"]
>>> print(" ".join(x))
Python Online Training

 


python return multiple values from functions

Python | Return multiple values from functions

>>> def A():
	return 2, 3, 4

>>> a, b, c = A()

>>> print(a, b, c)
2 3 4

 


Python Print String N times

Python | Print String N times

>>> s = 'Python'
>>> n = 5

>>> print(s * n)
PythonPythonPythonPythonPython

 


Python check the memory usage of an object

Python | Check the memory usage of  an object

>>> import sys
>>> x = 100

>>> print(sys.getsizeof(x))
28