How to write Pandas DataFrame to PostgreSQL table?
In this article, we will be looking at some methods to write Pandas dataframes to PostgreSQL tables in the Python.
Method 1: Using to_sql() function
to_sql function is used to write the given dataframe to a SQL database.
Syntax
df.to_sql('data', con=conn, if_exists='replace', index=False)
Parameters :
- data: name of the table.
- con: connection to the database.
- if_exists: if table exists or not. "replace" or "append".
- index: True or False.
Example:
In the example demonstrated below, we import the required packages and modules, establish a connection to the PostgreSQL database and convert the dataframe to PostgreSQL table by using the to_sql() method. Finally, all rows are fetched using fetchall() method.
To access the CSV file used click here.
# import packages
import psycopg2
import pandas as pd
from sqlalchemy import create_engine
# establish connections
conn_string = 'postgres://postgres:pass@127.0.0.1/Airlines_Database'
db = create_engine(conn_string)
conn = db.connect()
conn1 = psycopg2.connect(
database="Airlines_Database",
user='postgres',
password='pass',
host='127.0.0.1',
port= '5432'
)
conn1.autocommit = True
cursor = conn1.cursor()
# drop table if it already exists
cursor.execute('drop table if exists airlines_final')
sql = '''CREATE TABLE airlines_final(id int ,
day int ,airline char(20),destination char(20));'''
cursor.execute(sql)
# import the csv file to create a dataframe
data = pd.read_csv("airlines_final.csv")
data = data[["id","day","airline","destination"]]
# Create DataFrame
print(data)
# converting data to sql
data.to_sql('airlines_final', conn, if_exists= 'replace')
# fetching all rows
sql1='''select * from airlines_final;'''
cursor.execute(sql1)
for i in cursor.fetchall():
print(i)
conn1.commit()
conn1.close()
Output:
Method 2: Using execute_values() function
The execute_values() function from the psycopg2 library is used to get the postgres table of the given data frame.
Syntax:
psycopg2.extras.execute_values(cur, sql, argslist, template=None, page_size=100, fetch=False)
Parameters:
- cur – the cursor that will be used to run the query.
- sql – the query that will be run. A single percent s placeholder must be present, which will be substituted by a VALUES list.
- argslist — a list of series or dictionaries containing the query's arguments. The template must be followed in terms of font and content.
- template – the snippet that will be merged into each item in the argslist to form the query
- page size – the maximum amount of argslist items that each statement can have.
- fetch - it's similar to fetchall. the values can be "True" or "False"
Example:
In this example, the same CSV file is used in this method. code begins with importing packages, then we form a custom function execute_values, where the given dataframe, connection, and table name are given as arguments. The dataframe rows and values are updated into the PostgreSQL table using the execute_values() method. The defined method contains an exception handling block, if there's no exception "execute_values() done" is printed.
# import packages
import psycopg2
import psycopg2.extras as extras
import pandas as pd
def execute_values(conn, df, table):
tuples = [tuple(x) for x in df.to_numpy()]
cols = ','.join(list(df.columns))
# SQL query to execute
query = "INSERT INTO %s(%s) VALUES %%s" % (table, cols)
cursor = conn.cursor()
try:
extras.execute_values(cursor, query, tuples)
conn.commit()
except (Exception, psycopg2.DatabaseError) as error:
print("Error: %s" % error)
conn.rollback()
cursor.close()
return 1
print("execute_values() done")
cursor.close()
# establishing connection
conn = psycopg2.connect(
database="Airlines_Database",
user='postgres',
password='sherlockedisi',
host='127.0.0.1',
port='5432'
)
sql = '''CREATE TABLE airlines_final1(id int ,day
char(20) ,airline char(20),destination char(20));'''
# creating a cursor
cursor = conn.cursor()
cursor.execute(sql)
data = pd.read_csv("airlines_final.csv")
data = data[["id", "day", "airline", "destination"]]
# using the function defined
execute_values(conn, data, 'airlines_final1')
Output:
execute_values() done
