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How To Connect and run SQL queries to a PostgreSQL database from Python

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  • Last Updated : 21 Nov, 2022
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This article focus on connecting to a PostgreSQL database from Python.

Installation:

  • Install PostgreSQL, If you haven’t installed it.
  • We need to install the psycopg2 library to connect to a PostgreSQL database. Open the command prompt and run the below command to install psycopg2
pip3 install psycopg2

Creating a Database

You can create a Database in 2 Ways:

  1. Using pgAdmin 4 UI
  2. Using command

1. Using pgAdmin 4 UI

Go to pgAdmin and Follow these Steps.

  • Local_server[Right Click] -> Create -> Database 
Connect and run SQL queries to a PostgreSQL database from Python

Create Database from side menu pop-up

  • Next, Fill out the form Database:  WorkSpace and Save.

2. Create Database Using SQL query

Go to pgAdmin and follow these Steps:
Run the below Command in the Query tab

CREATE DATABASE WorkSpace;

Run the create database command

Connecting to the database

We need to connect to a PostgreSQL database using psycopg2.connect() function.

Where the attributes of connect() function are:

host = hostname,
dbname = databaseName,
user = username,
password = [Your Password],
port = [port_id]

In case you don’t know any of these connect() function attributes, you can follow the below steps:

 

 

Now You Know All the properties of this Database. Let’s continue.

Now, to connect to the database, we need to pass the attributes as arguments to the connect() function.

Syntax:

conn = psycopg2.connect(
    host = 'localhost',
    dbname = 'For_Practice',
    user = 'postgres',
    password = '[Password]',
    port = 5432
)

Create a cursor:

  • Create a cursor(i.e., curr) object and call its execute() method to execute queries.
  • Where execute() method is used to run a query that is passed as a string.

Syntax:

cur = conn.cursor()
cur.execute('[SQL queries]')

In the end, We need to save the changes using commit() method and finally close the opened connection using close() method.

Syntax:

conn.commit()
cur.close()

Python3




import psycopg2
  
conn = None
try:
    # connect to the PostgreSQL server
    print('Connecting to the PostgreSQL database...')
    conn = psycopg2.connect(
        host = 'localhost',
        dbname = 'For_Practice',
        user = 'postgres',
        password = '321654',
        port = 5432
    )
      
    # Creating a cursor with name cur.
    cur = conn.cursor()
    print('Connected to the PostgreSQL database')
      
    # Execute a query:
    # To display the PostgreSQL 
    # database server version
    cur.execute('SELECT version()')
    print(cur.fetchone())
      
    # Close the connection
    cur.close()
      
except(Exception, psycopg2.DatabaseError) as error:
    print(error)
finally:
    if conn is not None:
        conn.close()
        print('Database connection closed.')

Output:

 


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