Exploring cursor.execute in Python SQL Server: A Comprehensive Guide for Devs

Dear Dev, are you looking for ways to execute SQL queries in Python using SQL Server? If yes, then you have come to the right place. This article will guide you through the process of executing SQL queries using cursor.execute in Python with SQL Server.

Table of Contents

1. Introduction
2. Understanding Cursor and Cursor.execute
3. How to Connect to SQL Server from Python
4. Creating a Table in SQL Server
5. Inserting Data into a Table in SQL Server
6. Executing a Select Query using Cursor.execute
7. Executing a Select Query with Parameters using Cursor.execute
8. Executing an Insert Query using Cursor.execute
9. Executing an Update Query using Cursor.execute
10. Executing a Delete Query using Cursor.execute
11. Executing a Stored Procedure using Cursor.execute
12. Executing a Dynamic SQL Query using Cursor.execute
13. Transaction Management using Cursor.execute
14. Error Handling using Cursor.execute
15. Bulk Insertion using Cursor.execute
16. Fetching Multiple Rows using Cursor.execute
17. Fetching Single Row using Cursor.execute
18. Cursor Properties and Methods
19. Frequently Asked Questions
20. Conclusion

1. Introduction

Python is a popular language used for data analysis, web development, and many other applications. Microsoft SQL Server is one of the most widely used relational database management systems in the industry. Combining the power of Python and SQL Server can open many new opportunities for developers.

In this article, we will explore the Cursor.execute method in Python SQL Server. This method allows you to execute SQL queries in Python using the SQL Server database.

2. Understanding Cursor and Cursor.execute

Before we dive into the details of Cursor.execute, let’s understand what a cursor is. A cursor is a database object used to retrieve data from a database. In simple terms, a cursor acts as a pointer to a database result set.

The Cursor.execute method allows you to execute SQL queries using a cursor. The syntax for using this method is as follows:

cursor.execute(sql_query, params)

Here, sql_query is the SQL query you want to execute, and params are the parameters (if any) required by the query.

3. How to Connect to SQL Server from Python

Before we can execute SQL queries using Python, we need to establish a connection to the SQL Server database. In order to do so, we need to install the SQL Server driver for Python. This can be done using the following command:

!pip install pyodbc

Once the driver is installed, we can connect to the SQL Server database using the following code:

import pyodbc # Create a connection to the database conn = pyodbc.connect('DRIVER={SQL Server};SERVER=server_name;DATABASE=database_name;UID=username;PWD=password') # Create a cursor cursor = conn.cursor() 

Here, server_name is the name of the SQL Server instance, database_name is the name of the database you want to connect to, username is the SQL Server login name, and password is the SQL Server login password.

4. Creating a Table in SQL Server

Before we can insert data into a table, we need to create the table first. The following code creates a table named employees with two columns, id and name:

cursor.execute('CREATE TABLE employees(id INT PRIMARY KEY NOT NULL, name VARCHAR(50) NOT NULL)')

5. Inserting Data into a Table in SQL Server

Once the table has been created, we can insert data into it using the following code:

cursor.execute('INSERT INTO employees(id, name) VALUES (?, ?)', (1, 'John Doe'))

Here, ? is a placeholder for the parameter values. The values are passed as a tuple in the second parameter.

6. Executing a Select Query using Cursor.execute

The following code executes a select query to retrieve all rows from the employees table:

cursor.execute('SELECT * FROM employees') rows = cursor.fetchall()for row in rows:print(row.id, row.name)

The fetchall() method retrieves all rows from the result set. You can also use other methods like fetchone() to fetch a single row, or fetchmany(n) to fetch a specific number of rows.

7. Executing a Select Query with Parameters using Cursor.execute

Sometimes, you may need to execute a select query with parameters. The following code demonstrates how to do that:

id = 1 cursor.execute('SELECT * FROM employees WHERE id=?', (id,)) row = cursor.fetchone() print(row.id, row.name)

The ? placeholder is used to specify the parameter in the SQL query. The parameter value is passed as a tuple in the second parameter of the execute() method. Note that the comma after (id,) is required as it indicates that it is a tuple with one element.

8. Executing an Insert Query using Cursor.execute

We have already discussed how to insert data into a table. The following code demonstrates how to insert multiple rows into a table using a single insert query:

employees = [(2, 'Jane Smith'), (3, 'Bob Johnson'), (4, 'Sarah Wilson')] cursor.executemany('INSERT INTO employees(id, name) VALUES (?, ?)', employees)

The executemany() method is used to execute the same insert query for multiple rows. The parameters are passed as a list of tuples.

9. Executing an Update Query using Cursor.execute

The following code demonstrates how to update data in a table using the execute() method:

id = 1 new_name = 'Jane Doe' cursor.execute('UPDATE employees SET name=? WHERE id=?', (new_name, id))

The SET keyword is used to specify the new value, and the WHERE clause is used to specify the condition for updating the rows.

10. Executing a Delete Query using Cursor.execute

The following code demonstrates how to delete a row from a table using the execute() method:

id = 1 cursor.execute('DELETE FROM employees WHERE id=?', (id,))

The DELETE keyword is used to delete the specified rows from the table.

11. Executing a Stored Procedure using Cursor.execute

The following code demonstrates how to execute a stored procedure using the execute() method:

cursor.execute("{CALL stored_procedure_name(?, ?)}", (param1, param2)) 

The {CALL} keyword is used to specify that a stored procedure is being called. The parameter values are passed as a tuple in the second parameter of the execute() method.

12. Executing a Dynamic SQL Query using Cursor.execute

The following code demonstrates how to execute a dynamic SQL query using the execute() method:

table_name = 'employees' column_name = 'name' value = 'John Doe' sql_query = "SELECT * FROM {} WHERE {}='{}'".format(table_name, column_name, value) cursor.execute(sql_query) rows = cursor.fetchall()for row in rows:print(row.id, row.name)

The format() method is used to construct the SQL query. The curly braces are used as placeholders for the table name, column name, and value.

13. Transaction Management using Cursor.execute

The following code demonstrates how to use transaction management with the execute() method:

try:cursor.execute('BEGIN TRANSACTION')cursor.execute('INSERT INTO employees(id, name) VALUES (?, ?)', (5, 'Mary Brown'))cursor.execute('COMMIT')except:cursor.execute('ROLLBACK')

The BEGIN TRANSACTION keyword is used to start a transaction, and the COMMIT keyword is used to commit the changes. If an error occurs, the ROLLBACK keyword is used to undo the changes.

14. Error Handling using Cursor.execute

The following code demonstrates how to handle errors using the execute() method:

try:cursor.execute('INSERT INTO employees(id, name) VALUES (?, ?)', (6, ''))cursor.execute('COMMIT')except pyodbc.Error as ex:print("Error: ", ex)cursor.execute('ROLLBACK')

The try-except block is used to catch any errors that occur during the execution of the SQL query. The pyodbc.Error exception is raised when an error occurs. The ROLLBACK keyword is used to undo any changes made in case of an error.

15. Bulk Insertion using Cursor.execute

The following code demonstrates how to use bulk insertion with the execute() method:

import pandas as pd # Read data from a CSV file data = pd.read_csv('employees.csv') # Convert the data to a list of tuples data = [tuple(x) for x in data.to_numpy()] # Execute the bulk insert cursor.executemany('INSERT INTO employees(id, name) VALUES (?, ?)', data) 

The executemany() method is used to insert multiple rows into the table at once. The data is first read from a CSV file and converted to a list of tuples before being passed to the executemany() method.

16. Fetching Multiple Rows using Cursor.execute

The following code demonstrates how to fetch multiple rows using the execute() method:

cursor.execute('SELECT * FROM employees') rows = cursor.fetchmany(2)for row in rows:print(row.id, row.name)

The fetchmany(n) method is used to retrieve a specific number of rows from the result set.

17. Fetching Single Row using Cursor.execute

The following code demonstrates how to fetch a single row using the execute() method:

id = 1 cursor.execute('SELECT * FROM employees WHERE id=?', (id,)) row = cursor.fetchone() print(row.id, row.name)

The fetchone() method is used to retrieve a single row from the result set.

18. Cursor Properties and Methods

The following code demonstrates some of the useful properties and methods of the cursor object:

cursor.rowcount # Returns the number of rows affected by the last SQL statement cursor.description # Returns information about the columns returned by the last SQL querycursor.arraysize # Specifies the number of rows to fetch at a timecursor.close() # Closes the cursorconn.close() # Closes the connection

The rowcount property returns the number of rows affected by the last SQL statement. The description property returns information about the columns returned by the last SQL query. The arraysize property specifies the number of rows to fetch at a time. The close() method is used to close the cursor and the connection.

19. Frequently Asked Questions

20. Conclusion

Cursor.execute is a powerful method that allows you to execute SQL queries in Python using SQL Server. In this article, we covered various aspects of using Cursor.execute, including connecting to SQL Server from Python, creating and manipulating tables, executing queries with parameters, and managing transactions and errors.

We also explored some of the frequently asked questions about Cursor.execute. We hope this article has provided you with a comprehensive understanding of how to use Cursor.execute in your Python SQL Server projects.