PostgreSQL Python: Insert Data Into a Table

Summary: in this tutorial, you will learn to insert one or more rows into a PostgreSQL table from Python.

This tutorial picks up from where the Creating Tables Tutorial left off.

Steps for inserting one row into a table from Python

To insert one or more rows into a table from Python, you follow these steps:

First, connect to the PostgreSQL server.
Next, create a cursor object from the connection object.
Then, execute the INSERT statement with values by calling the execute() or executemany() method of the cursor object.
After that, commit the transaction by calling the commit() method of the connection object.
Finally, obtain the inserted ID by calling the fetchone() method of the cursor object.

Inserting data into a table example

We will use the vendors table in the suppliers database for the demonstration purposes:

[画像:vendors_table]

1) Inserting one row into a table

First, create a new file named insert.py.

Second, define a insert_vendor() function in the insert.py file:

import psycopg2
from config import load_config


def insert_vendor(vendor_name):
 """ Insert a new vendor into the vendors table """

 sql = """INSERT INTO vendors(vendor_name)
 VALUES(%s) RETURNING vendor_id;"""

 vendor_id = None
 config = load_config()

 try:
 with psycopg2.connect(**config) as conn:
 with conn.cursor() as cur:
 # execute the INSERT statement
 cur.execute(sql, (vendor_name,))

 # get the generated id back
 rows = cur.fetchone()
 if rows:
 vendor_id = rows[0]

 # commit the changes to the database
 conn.commit()
 except (Exception, psycopg2.DatabaseError) as error:
 print(error)
 finally:
 return vendor_id


if __name__ == '__main__':
 insert_vendor("3M Co.")

The insert_vendor() function will insert a new row into the vendors table and return the inserted vendor_id.

2) Inserting multiple rows into a table

The steps for inserting multiple rows into a table are similar to the steps for inserting one row.

The key difference is in the third step: instead of calling the execute() method of the cursor object, you use the executemany() method.

For example, the following defines insert_many_vendors() function that inserts multiple rows into the vendors table:

def insert_many_vendors(vendor_list):
 """ Insert multiple vendors into the vendors table """

 sql = "INSERT INTO vendors(vendor_name) VALUES(%s) RETURNING *"
 config = load_config()
 try:
 with psycopg2.connect(**config) as conn:
 with conn.cursor() as cur:
 # execute the INSERT statement
 cur.executemany(sql, vendor_list)

 # commit the changes to the database
 conn.commit()
 except (Exception, psycopg2.DatabaseError) as error:
 print(error)

The following uses the insert_vendor() and insert_many_vendors() functions to insert one and multiple rows into the vendors table:

if __name__ == '__main__':
 insert_vendor("3M Co.")

 insert_many_vendors([
 ('AKM Semiconductor Inc.',),
 ('Asahi Glass Co Ltd.',),
 ('Daikin Industries Ltd.',),
 ('Dynacast International Inc.',),
 ('Foster Electric Co. Ltd.',),
 ('Murata Manufacturing Co. Ltd.',)
 ])

3) Execute the insert.py module

First, open the Command Prompt on Windows or Terminal on Unix-like systems.

Second, run the following command to execute the insert.py module:

python insert.py

4) Verify the inserts

First, connect to the PostgreSQL server using the psql:

psql -U postgres

Second, change the current database to suppliers:

\c suppliers

Third, retrieve data from the vendors table:

SELECT * FROM vendors;

Output:

vendor_id | vendor_name
-----------+-------------------------------
 1 | 3M Co.
 2 | AKM Semiconductor Inc.
 3 | Asahi Glass Co Ltd.
 4 | Daikin Industries Ltd.
 5 | Dynacast International Inc.
 6 | Foster Electric Co. Ltd.
 7 | Murata Manufacturing Co. Ltd.
(7 rows)

Download the project source code

Summary

Use the execute() or executemany() method of the cursor object to insert one or more rows into a table from Python.