Run raw SQL query in python

This recipe unlock full power of SQL, right here you can flex all your muscles and break your caps lock key.

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Documentation

All required packages are automatically imported by MLJAR Studio for you so you don't have to worry about them.

# import packages
import psycopg
import os
from dotenv import load_dotenv

Make sure you opened a connection in your notebook. To learn how to do it, check out open and test database connection example notebook.

# load credentials from .env file:
load_dotenv(override=True)

# get the credentials
def create_new_connection():
    try:
        conn = psycopg.connect(
            dbname=os.getenv("POSTGRES_DB_NAME"),
            user=os.getenv("POSTGRES_USERNAME"),
            password=os.getenv("POSTGRES_PASSWORD"),
            host=os.getenv("POSTGRES_HOST"),
            port=os.getenv("POSTGRES_PORT"),
        )
        return conn
    # check for errors
    except psycopg.Error as e:
        raise psycopg.Error(f"""
Error occurred while establishing connection: 
    {e}

Maybe you provided wrong credentials, use define new connection recipe to edit them.
Other option is that database server is down or you dont have the right acces to this database.
            """)

# open new connection:
conn = create_new_connection()

With raw query you can do whatever you want. You are limited only by your imagination and SQL syntax. Here we will settle for simple and classic SELECT *.

# if connection was used and closed it is reopen here
if conn.closed:
    conn = create_new_connection()

# run query
with conn:
    with conn.cursor() as cur:

        try:
            cur.execute("""
SELECT 1
            """)
        # check for errors
        except psycopg.ProgrammingError as e:
            raise psycopg.ProgrammingError(f"""
Problem running query:
    {e}
            """)

        # check if query was a select query
        if (str(cur.statusmessage).upper().startswith("SELECT")):

            # print the results
            for result in cur.fetchall():
                print(f"{result}")

Conclusions

Raw query is very powerful but requires knowledge of SQL, you can look at other database recipes and have a guess how to write your own queries. If you are experienced user this should be the place right for you.

Recipes used in the postgresql-python-raw-query.ipynb

All code recipes used in this notebook are listed below. You can click them to check their documentation.

Packages used in the postgresql-python-raw-query.ipynb

List of packages that need to be installed in your Python environment to run this notebook. Please note that MLJAR Studio automatically installs and imports required modules for you.

psycopg>=3.2.1

python-dotenv>=1.0.1

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