Execute PostgreSQL Stored Procedure and Function in Python

In this lesson, you will learn how to execute a PostgreSQL function and Stored procedure in Python. PostgreSQL function can perform different operations; it can be data manipulation or data retrieval. Let’s see how to execute such functions from Python.

Prerequisites

Before executing the following program, please make sure you have the following in place:

• Username and password that you need to connect to PostgreSQL.
• PostgreSQL database Stored procedure or function name which you want to execute.

For this lesson, I have created a function get_production_Deployment in PostgreSQL, which returns a list of employee records who deployed code changes in the production environment.

CREATE OR REPLACE FUNCTION get_production_deployment(appId integer)
  RETURNS TABLE(empId INTEGER, empName VARCHAR, designation VARCHAR) AS
$
BEGIN
 RETURN QUERY
 
 SELECT employee.id, employee.name, employee.designation
 FROM employee where employee.id = 
 (SELECT empId FROM prod_movement where prod_movement.appId = appId)

END; $
 
LANGUAGE plpgsql;

Steps to call PostgreSQL Function and stored procedure from Python

We are using a psycopg2 module to execute the PostgreSQL function in Python.

Example to execute PostgreSQL Function and stored procedure

Let see the demo now. We already created the stored procedure get_production_Deployment, which accepts the application id as an IN parameter and returning its employee id, employee name, and designation as the OUT parameters.

import psycopg2

try:
    ps_connection = psycopg2.connect(user="postgres",
                                     password="pass@#29",
                                     host="127.0.0.1",
                                     port="5432",
                                     database="postgres_db")

    cursor = ps_connection.cursor()

    # call stored procedure
    cursor.callproc('get_production_Deployment', [72, ])

    print("fechting Employee details who pushed changes to the production from function")
    result = cursor.fetchall()
    for row in result:
        print("Id = ", row[0], )
        print("Name = ", row[1])
        print("Designation  = ", row[2])

except (Exception, psycopg2.DatabaseError) as error:
    print("Error while connecting to PostgreSQL", error)

finally:
    # closing database connection.
    if ps_connection:
        cursor.close()
        ps_connection.close()
        print("PostgreSQL connection is closed")

Output:

fechting Employee details who pushed changes to the production from function
Id =  23
Name =  Scot
Designation =  Application Developer
PostgreSQL connection is closed

We can also use Python cursor’s fetchall(), fetchmany(), fetchone() methods depending on the return value from a function or a stored procedure.

Also, cursor.callproc() internally uses execute() method of the cursor object to call a stored procedure. So you can directly execute the following query to call stored procedure instead of using cursor.callproc()

cursor.execute("SELECT * FROM get_production_Deployment( %s); ", (appId, ))

Next Steps:

To practice what you learned in this article, Please solve a Python Database Exercise project to Practice and master the Python Database operations.