PL/Python is a procedural language for PostgreSQL that allows you to write stored procedures, triggers, and functions in Python. The PL/Python language is implemented as an extension module for PostgreSQL, which means that it’s not part of the core PostgreSQL system but is instead loaded as an add-on.
Here’s a brief overview of how PL/Python is implemented in PostgreSQL:
- The PL/Python extension module is loaded into PostgreSQL using the CREATE EXTENSION command:
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CREATE EXTENSION plpython3u; |
This command will load the PL/Python extension module into PostgreSQL and make it available for use.
- You can then create a PL/Python function using the CREATE FUNCTION command. Here’s an example of a simple PL/Python function that returns the sum of two numbers:
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CREATE OR REPLACE FUNCTION sum(a INTEGER, b INTEGER) RETURNS INTEGER AS $$ return a + b $$ LANGUAGE plpython3u; |
In this example, the function takes two integer arguments, adds them together using Python’s + operator, and returns the result. The function is declared as using the PL/Python language by specifying LANGUAGE plpython3u.
- Once the function has been created, you can call it from within PostgreSQL using the SELECT statement:
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SELECT sum(1, 2); |
This statement will call the sum function and return the result, which is 3 in this case.
PL/Python also allows you to interact with the PostgreSQL database from within your Python code. Here’s an example of a PL/Python function that uses the psycopg2 library to connect to the database and retrieve some data:
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CREATE OR REPLACE FUNCTION get_employee_name(employee_id INTEGER) RETURNS TEXT AS $$ import psycopg2 conn = psycopg2.connect(dbname='mydatabase', user='myuser', password='mypassword', host='localhost') cur = conn.cursor() cur.execute("SELECT name FROM employees WHERE id = %s", [employee_id]) result = cur.fetchone() cur.close() conn.close() return result[0] $$ LANGUAGE plpython3u; |
In this example, the function connects to the mydatabase database using the psycopg2 library, executes a SELECT statement to retrieve the name of the employee with the given employee_id, and returns the name as a string. Note that this function is still declared as using the PL/Python language, even though it includes Python code that interacts with the database.
Overall, PL/Python allows you to write powerful, flexible stored procedures, triggers, and functions using the Python programming language, while still being able to take advantage of the capabilities of the PostgreSQL database system.