Querying mysql with python

Python Select from MySQL Table

This article demonstrates how to select rows of a MySQL table in Python.

You’ll learn the following MySQL SELECT operations from Python using a ‘MySQL Connector Python’ module.

• Execute the SELECT query and process the result set returned by the query in Python.
• Use Python variables in a where clause of a SELECT query to pass dynamic values.
• Use fetchall() , fetchmany() , and fetchone() methods of a cursor class to fetch all or limited rows from a table.

Further Reading:

Table of contents

Prerequisites

Before moving further, Please make sure you have the following in place: –

• Username and password to connect MySQL
• MySQL table name from which you want to select data.

For this lesson, I am using a ‘Laptop’ table present in my MySQL server.

If a table is not present in your MySQL server, you can refer to our article to create a MySQL table from Python.

You can also download a SQL query file, which contains SQL queries for table creation and data so that you can use this table for your INSERT operations.

Steps to fetch rows from a MySQL database table

How to Select from a MySQL table using Python

1. Connect to MySQL from Python Refer to Python MySQL database connection to connect to MySQL database from Python using MySQL Connector module
2. Define a SQL SELECT Query Next, prepare a SQL SELECT query to fetch rows from a table. You can select all or limited rows based on your requirement. If the where condition is used, then it decides the number of rows to fetch.
   For example, SELECT col1, col2,…colnN FROM MySQL_table WHERE >. This will return row number 10.
3. Get Cursor Object from Connection Next, use a connection.cursor() method to create a cursor object. This method creates a new MySQLCursor object.
4. Execute the SELECT query using execute() method Execute the select query using the cursor.execute() method.
5. Extract all rows from a result After successfully executing a Select operation, Use the fetchall() method of a cursor object to get all rows from a query result. it returns a list of rows.
6. Iterate each row Iterate a row list using a for loop and access each row individually (Access each row’s column data using a column name or index number.)
7. Close the cursor object and database connection object use cursor.clsoe() and connection.clsoe() method to close open connections after your work completes.

In this example, we are fetching all the rows from the Laptop table and copying them into Python variables so we can use it in our program.

import mysql.connector try: connection = mysql.connector.connect(host='localhost', database='electronics', user='pynative', password='pynative@#29') sql_select_Query = "select * from Laptop" cursor = connection.cursor() cursor.execute(sql_select_Query) # get all records records = cursor.fetchall() print("Total number of rows in table: ", cursor.rowcount) print("\nPrinting each row") for row in records: print("Id = ", row[0], ) print("Name = ", row[1]) print("Price = ", row[2]) print("Purchase date = ", row[3], "\n") except mysql.connector.Error as e: print("Error reading data from MySQL table", e) finally: if connection.is_connected(): connection.close() cursor.close() print("MySQL connection is closed")

Total number of rows in Laptop is: 7 Printing each laptop record Id = 1 Name = Lenovo ThinkPad P71 Price = 6459.0 Purchase date = 2019-08-14 Id = 2 Name = Area 51M Price = 6999.0 Purchase date = 2019-04-14 Id = 3 Name = MacBook Pro Price = 2499.0 Purchase date = 2019-06-20 Id = 4 Name = HP Pavilion Power Price = 1999.0 Purchase date = 2019-01-11 Id = 5 Name = MSI WS75 9TL-496 Price = 5799.0 Purchase date = 2019-02-27 Id = 6 Name = Microsoft Surface Price = 2330.0 Purchase date = 2019-07-23 Id = 7 Name = Acer Predator Triton Price = 2435.0 Purchase date = 2019-08-15 MySQL connection is closed

Note: Use the following methods to fetch data returned by a cursor.execute()

• cursor.fetchall() to fetch all rows
• cursor.fetchone() to fetch a single row
• cursor.fetchmany(SIZE) to fetch limited rows

Use Python variables as parameters in MySQL Select Query

We often need to pass variables to SQL select query in where clause to check some conditions. Let’s say the application wants to fetch laptop price by giving any laptop id at runtime. To handle such a requirement, we need to use a parameterized query.

A parameterized query is a query in which placeholders ( %s ) are used for parameters and the parameter values supplied at execution time.

cursor.execute("SELECT Price FROM Laptop WHERE )

import mysql.connector def get_laptop_detail(id): try: connection = mysql.connector.connect(host='localhost', database='electronics', user='pynative', password='pynative@#29') cursor = connection.cursor() sql_select_query = """select * from laptop where # set variable in query cursor.execute(sql_select_query, (id,)) # fetch result record = cursor.fetchall() for row in record: print("Id = ", row[0], ) print("Name = ", row[1]) print("Join Date = ", row[2]) print("Salary = ", row[3], "\n") except mysql.connector.Error as error: print("Failed to get record from MySQL table: <>".format(error)) finally: if connection.is_connected(): cursor.close() connection.close() print("MySQL connection is closed") get_laptop_detail(1) get_laptop_detail(2)

Id = 1 Name = Lenovo ThinkPad P71 Join Date = 6459.0 Salary = 2019-08-14 connection is closed Id = 2 Name = Area 51M Join Date = 6999.0 Salary = 2019-04-14 MySQL connection is closed

Select limited rows from MySQL table using fetchmany and fetchone

In some situations, fetching all the rows from a table is a time-consuming task if a table contains thousands of rows.

If we fetch all rows, we need more space and processing time. So it is essentials to use the fetchmany() method of cursor class to fetch fewer rows.

Syntax of the cursor’s fetchmany()

rows = cursor.fetchmany(size=row_size)

Cursor’s fetchmany() methods return the number of rows specified by size argument, defaults value of size argument is one. For example, if the specified size is 5, then it returns five rows.

Note: If a table contains a row lesser than the specified size, then fewer rows are returned.

Syntax of fetchone()

This method fetches the next set of rows of a query result and returns a list of tuples. If no more rows are available, it returns an empty list.

This method returns a single record or None if no more rows are available.

The fetchone() method is internally used by a fetchall() and fetchmany() to fetch rows.

Example to fetch fewer rows from MySQL table using cursor’s fetchmany

import mysql.connector from mysql.connector import Error try: connection = mysql.connector.connect(host='localhost', database='electronics', user='pynative', password='pynative@#29') mySql_select_Query = "select * from laptop" cursor = connection.cursor() cursor.execute(mySql_select_Query) row_count = 2 records = cursor.fetchmany(row_count) print("Total number of rows is: ", cursor.rowcount) print("Printing ", row_count, " Laptop record using cursor.fetchmany") for row in records: print(row) except Error as e: print("Error while connecting to MySQL", e) finally: if connection.is_connected(): cursor.close() connection.close() print("connection is closed") 

Total number of rows is: 2 Printing 2 Laptop record using cursor.fetchmany (1, 'Lenovo ThinkPad P71', 6459.0, datetime.date(2019, 8, 14)) (2, 'Area 51M', 6999.0, datetime.date(2019, 4, 14))

Note: If you are getting MySQL Unread result error set buffered=True in connection like connection.cursor(buffered=True) .

Fetch single row from MySQL table using cursor’s fetchone

import mysql.connector try: connection = mysql.connector.connect(host='localhost', database='electronics', user='pynative', password='pynative@#29') mySql_select_Query = "select * from laptop" cursor = connection.cursor(buffered=True) cursor.execute(mySql_select_Query) record = cursor.fetchone() print(record) except mysql.connector.Error as error: print("Error while connecting to MySQL", error) finally: if connection.is_connected(): cursor.close() connection.close() print("MySQL connection is closed")

Printing first record (1, 'Lenovo ThinkPad P71', 6459.0, datetime.date(2019, 8, 14)) MySQL connection is closed

Python Fetch MySQL row using the column names

You can also retrieve result using columns names instead of id. For example, you would like to do something like this.

records = cursor.fetchall() for row in records: val1 = row["columnName1"], ) val2 = row["columnName2"]) val3 = row["columnName3"])

If you try to fetch data using column name directly, you will receive a TypeError: tuple indices must be integers or slices, not str .

To select records from my MySQL table using a column name, we only need to change the cursor creation. Replace the standard cursor creation with the following code, and you are ready to fetch records from my MySQL table using a column name.

cursor = connection.cursor(dictionary=True)

Why set dictionary=True ? because MySQLCursorDict creates a cursor that returns rows as dictionaries so we can access using column name (here column name is the key of the dictionary)

In the following example, I have selected all the records from my MySQL table using a column name instead of the column’s integer index.

import mysql.connector from mysql.connector import Error try: connection = mysql.connector.connect(host='localhost', database='Electronics', user='pynative', password='pynative@#29') sql_select_Query = "select * from Laptop" # MySQLCursorDict creates a cursor that returns rows as dictionaries cursor = connection.cursor(dictionary=True) cursor.execute(sql_select_Query) records = cursor.fetchall() print("Fetching each row using column name") for row in records: name = row["Name"] price = row["Price"] purchase_date = row["Purchase_date"] print(id, name, price, purchase_date) except Error as e: print("Error reading data from MySQL table", e) finally: if connection.is_connected(): connection.close() cursor.close() print("MySQL connection is closed") 

Fetching each row using column name 1 Lenovo ThinkPad P71 6459.0 2019-08-14 2 Area 51M 6999.0 2019-04-14 3 MacBook Pro 2499.0 2019-06-20 4 HP Pavilion Power 1999.0 2019-01-11 5 MSI WS75 9TL-496 5799.0 2019-02-27 6 Microsoft Surface 2330.0 2019-07-23 7 Acer Predator Triton 2435.0 2019-08-17 10 Lenovo ThinkPad P71 6459.0 2019-08-14 11 Lenovo ThinkPad P71 6459.0 2019-08-14 MySQL connection is closed

Select MySQL column value into a Python Variable

Let’s see how to execute the following SELECT SQL Query and store the table’s column value into a Python variable for further processing.

Ig you execute the below code you will get .

cursor.execute("SELECT Price FROM Laptop WHERE (cursor.fetchone() )

You can get the output like

Let’s see how to extract just the column value (7000) and save it in a variable to do some calculations so you can give a 10% discount on it.

import mysql.connector try: connection = mysql.connector.connect(host='localhost', database='electronics', user='pynative', password='pynative@#29') sql_Query = "select price from laptop where cursor = connection.cursor() cursor.execute(sql_Query, id) record = cursor.fetchone() # selecting column value into variable price = float(record[0]) print("Laptop price is : ", price) except mysql.connector.Error as error: print("Failed to get record from database: <>".format(error)) finally: if connection.is_connected(): cursor.close() connection.close() print("MySQL connection is closed") 

Laptop price is : 6459.0 MySQL connection is closed

Let’s understand this example:

• You can see in the above example after fetching a row using a cursor.fetchone() we converted column value to appropriate type using value = float(record[0]) .
• We retrieved the 0th index value from the result set.

Next Steps:

To practice what you learned in this article, Please solve a Python Database Exercise project to Practice and master the Python Database operations.

Did you find this page helpful? Let others know about it. Sharing helps me continue to create free Python resources.

About Vishal

I’m Vishal Hule, Founder of PYnative.com. I am a Python developer, and I love to write articles to help students, developers, and learners. Follow me on Twitter

Related Tutorial Topics:

Python Exercises and Quizzes

Free coding exercises and quizzes cover Python basics, data structure, data analytics, and more.

• 15+ Topic-specific Exercises and Quizzes
• Each Exercise contains 10 questions
• Each Quiz contains 12-15 MCQ

Источник