kopia lustrzana https://github.com/animator/learn-python
Ankit Mahato
GitHub
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# List of sections
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- [Section title](filename.md)
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- [Introduction to MySQL and Queries](intro_mysql_queries.md)
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# Introduction to MySQL Queries
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MySQL is a widely-used open-source relational database management system (RDBMS) that utilizes SQL (Structured Query Language) for managing and querying data. In Python, the **mysql-connector-python** library allows you to connect to MySQL databases and execute SQL queries, providing a way to interact with the database from within a Python program.
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## Prerequisites
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* Python and MySQL Server must be installed and configured.
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* The library: **mysql-connector-python** must be installed.
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## Establishing connection with server
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To establish a connection with the MySQL server, you need to import the **mysql.connector** module and create a connection object using the **connect()** function by providing the prompt server details as mentioned.
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```python
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import mysql.connector
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con = mysql.connector.connect(
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host ="localhost",
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user ="root",
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passwd ="12345"
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)
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print((con.is_connected()))
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```
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Having established a connection with the server, you get the following output :
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```
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True
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```
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## Creating a Database [CREATE]
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To create a database, you need to execute the **CREATE DATABASE** query. The following code snippet demonstrates how to create a database named **GSSOC**.
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```python
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import mysql.connector
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# Establish the connection
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conn = mysql.connector.connect(
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host="localhost",
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user="root",
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password="12345"
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)
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# Create a cursor object
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cursor = conn.cursor()
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# Execute the query to show databases
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cursor.execute("SHOW DATABASES")
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# Fetch and print the databases
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databases = cursor.fetchall()
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for database in databases:
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print(database[0])
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# Execute the query to create database GSSOC
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cursor.execute("CREATE DATABASE GSSOC")
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print("\nAfter creation of the database\n")
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# Execute the query to show databases
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cursor.execute("SHOW DATABASES")
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# Fetch and print the databases
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databases = cursor.fetchall()
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for database in databases:
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print(database[0])
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cursor.close()
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conn.close()
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```
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You can observe in the output below, after execution of the query a new database named **GSSOC** has been created.
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#### Output:
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```
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information_schema
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mysql
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performance_schema
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sakila
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sys
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world
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After creation of the database
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gssoc
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information_schema
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mysql
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performance_schema
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sakila
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sys
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world
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```
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## Creating a Table in the Database [CREATE]
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Now, we will create a table in the database. We will create a table named **example_table** in the database **GSSOC**. We will execute **CREATE TABLE** query and provide the fields for the table as mentioned in the code below:
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```python
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import mysql.connector
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# Establish the connection
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conn = mysql.connector.connect(
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host="localhost",
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user="root",
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password="12345"
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)
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# Create a cursor object
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cursor = conn.cursor()
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# Execute the query to show tables
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cursor.execute("USE GSSOC")
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cursor.execute("SHOW TABLES")
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# Fetch and print the tables
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tables = cursor.fetchall()
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print("Before creation of table\n")
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for table in tables:
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print(table[0])
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create_table_query = """
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CREATE TABLE example_table (
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name VARCHAR(255) NOT NULL,
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age INT NOT NULL,
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email VARCHAR(255)
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)
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"""
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# Execute the query
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cursor.execute(create_table_query)
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# Commit the changes
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conn.commit()
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print("\nAfter creation of Table\n")
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# Execute the query to show tables in GSSOC
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cursor.execute("SHOW TABLES")
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# Fetch and print the tables
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tables = cursor.fetchall()
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for table in tables:
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print(table[0])
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cursor.close()
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conn.close()
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```
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#### Output:
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```
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Before creation of table
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After creation of Table
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example_table
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```
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## Inserting Data [INSERT]
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To insert data in an existing table, the **INSERT INTO** query is used, followed by the name of the table in which the data needs to be inserted. The following code demonstrates the insertion of multiple records in the table by **executemany()**.
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```python
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import mysql.connector
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# Establish the connection
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conn = mysql.connector.connect(
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host="localhost",
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user="root",
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password="12345"
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)
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# Create a cursor object
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cursor = conn.cursor()
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cursor.execute("USE GSSOC")
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# SQL query to insert data
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insert_data_query = """
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INSERT INTO example_table (name, age, email)
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VALUES (%s, %s, %s)
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"""
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# Data to be inserted
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data_to_insert = [
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("John Doe", 28, "john.doe@example.com"),
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("Jane Smith", 34, "jane.smith@example.com"),
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("Sam Brown", 22, "sam.brown@example.com")
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]
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# Execute the query for each data entry
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cursor.executemany(insert_data_query, data_to_insert)
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conn.commit()
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cursor.close()
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conn.close()
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```
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## Displaying Data [SELECT]
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To display the data from a table, the **SELECT** query is used. The following code demonstrates the display of data from the table.
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```python
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import mysql.connector
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# Establish the connection
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conn = mysql.connector.connect(
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host="localhost",
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user="root",
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password="12345"
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)
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# Create a cursor object
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cursor = conn.cursor()
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cursor.execute("USE GSSOC")
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# SQL query to display data
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display_data_query = "SELECT * FROM example_table"
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# Execute the query for each data entry
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cursor.execute(display_data_query)
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# Fetch all the rows
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rows = cursor.fetchall()
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# Print the column names
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column_names = [desc[0] for desc in cursor.description]
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print(column_names)
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# Print the rows
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for row in rows:
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print(row)
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cursor.close()
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conn.close()
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```
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#### Output :
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```
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['name', 'age', 'email']
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('John Doe', 28, 'john.doe@example.com')
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('Jane Smith', 34, 'jane.smith@example.com')
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('Sam Brown', 22, 'sam.brown@example.com')
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```
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## Updating Data [UPDATE]
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To update data in the table, **UPDATE** query is used. In the following code, we will be updating the email and age of the record where the name is John Doe.
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```python
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import mysql.connector
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# Establish the connection
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conn = mysql.connector.connect(
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host="localhost",
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user="root",
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password="12345"
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)
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# Create a cursor object
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cursor = conn.cursor()
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cursor.execute("USE GSSOC")
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# SQL query to display data
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display_data_query = "SELECT * FROM example_table"
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# SQL Query to update data of John Doe
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update_data_query = """
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UPDATE example_table
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SET age = %s, email = %s
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WHERE name = %s
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"""
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# Data to be updated
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data_to_update = (30, "new.email@example.com", "John Doe")
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# Execute the query
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cursor.execute(update_data_query, data_to_update)
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# Commit the changes
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conn.commit()
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# Execute the query for each data entry
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cursor.execute(display_data_query)
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# Fetch all the rows
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rows = cursor.fetchall()
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# Print the column names
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column_names = [desc[0] for desc in cursor.description]
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print(column_names)
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# Print the rows
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for row in rows:
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print(row)
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cursor.close()
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conn.close()
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```
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#### Output:
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```
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['name', 'age', 'email']
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('John Doe', 30, 'new.email@example.com')
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('Jane Smith', 34, 'jane.smith@example.com')
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('Sam Brown', 22, 'sam.brown@example.com')
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```
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## Deleting Data [DELETE]
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In this segment, we will Delete the record named "John Doe" using the **DELETE** and **WHERE** statements in the query. The following code explains the same and the observe the change in output.
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```python
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import mysql.connector
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# Establish the connection
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conn = mysql.connector.connect(
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host="localhost",
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user="root",
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password="12345"
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)
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# Create a cursor object
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cursor = conn.cursor()
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cursor.execute("USE GSSOC")
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# SQL query to display data
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display_data_query = "SELECT * FROM example_table"
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# SQL query to delete data
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delete_data_query = "DELETE FROM example_table WHERE name = %s"
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# Data to be deleted
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data_to_delete = ("John Doe",)
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# Execute the query
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cursor.execute(delete_data_query, data_to_delete)
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# Commit the changes
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conn.commit()
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# Execute the query for each data entry
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cursor.execute(display_data_query)
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# Fetch all the rows
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rows = cursor.fetchall()
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# Print the column names
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column_names = [desc[0] for desc in cursor.description]
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print(column_names)
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# Print the rows
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for row in rows:
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print(row)
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cursor.close()
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conn.close()
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```
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#### Output:
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```
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['name', 'age', 'email']
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('Jane Smith', 34, 'jane.smith@example.com')
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('Sam Brown', 22, 'sam.brown@example.com')
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```
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## Deleting the Table/Database [DROP]
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For deleting a table, you can use the **DROP** query in the following manner:
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```python
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import mysql.connector
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# Establish the connection
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conn = mysql.connector.connect(
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host="localhost",
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user="root",
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password="12345"
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)
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# Create a cursor object
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cursor = conn.cursor()
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cursor.execute("USE GSSOC")
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# SQL query to delete the table
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delete_table_query = "DROP TABLE IF EXISTS example_table"
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# Execute the query
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cursor.execute(delete_table_query)
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# Verify the table deletion
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cursor.execute("SHOW TABLES LIKE 'example_table'")
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result = cursor.fetchone()
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cursor.close()
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conn.close()
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if result:
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print("Table deletion failed.")
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else:
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print("Table successfully deleted.")
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```
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#### Output:
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```
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Table successfully deleted.
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```
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Similarly, you can delete the database also by using the **DROP** and accordingly changing the query to be executed.
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