Reading from databases with Python

Articles From: TheAutomatic.net
Website: TheAutomatic.net

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Blogger, TheAutomatic.net, and Senior Data Scientist

Background – Reading from Databases with Python

This post will talk about several packages for working with databases using Python. We’ll start by covering pyodbc, which is one of the more standard packages used for working with databases, but we’ll also cover a very useful module called turbodbc, which allows you to run SQL queries efficiently (and generally faster) within Python.

pyodbc

pyodbc can be installed using pip:

pip install pyodbc

Let’s start by writing a simple SQL query using pyodbc. To do that, we first need to connect to a specific database. In the examples laid out here, we will be using a SQLite database on my machine. However, you can do this with many other database systems, as well, such as SQL Server, MySQL, Oracle, etc. In the connection string, we specify the database driver (e.g. one of the database systems mentioned), the server, database name, and potentially username / password. If you have a trusted connection setup, then you can specify that (like in the first example below).

import pyodbc

channel = pyodbc.connect(“DRIVER={SQLite3 ODBC Driver};SERVER=localhost;DATABASE=sample_database.db;Trusted_connection=yes”)

# or if using a password

channel = pyodbc.connect(“DRIVER={SQLite3 ODBC Driver};SERVER=localhost;DATABASE=sample_database.db;Uid=YourUsername;Pwd=YourPassword;'”)

Reading SQL query with pandas

After we’ve made the connection, we can write a SQL query to retrieve data from this database. One way of doing that is using the pandas package. Below, we wrap the SQL code inside quotes as the first parameter of pd.read_sql. The second parameter contains our connection object.

import pandas as pd

pd.read_sql(“select * from sample_table;”, channel)

Reading SQL query with pyodbc

Besides using pandas, we can execute a SQL query with pyodbc alone. In this case, we need to create a cursor object. A cursor is an object used to process the results of a SQL query.

cursor = channel.cursor()

cursor.execute(“select * from sample_table;”)

Next, we can extract the results of the query by using the fetchall method. fetchall returns the rows of the query result into a list, rather than a data frame. Each element in the list corresponds to a row.

rows = cursor.fetchall()

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