Exporting a PostgreSQL query to a csv file using Python

Question

I need to export some rows from a table in a PostgreSQL database to a .csv file using a Python script:

#!/usr/bin/python
# -*- coding: utf-8 -*-

import sys, psycopg2

...

    conn = psycopg2.connect("dbname=dbname user=user password=password")
    cur = conn.cursor()

    sql = "copy (SELECT * FROM table WHERE month=6) TO '/mnt/results/month/table.csv' WITH CSV DELIMITER ';';"
    cur.execute(sql)
    cur.close()

...

But when I run the script I get this:

Syntax error at or near «»
LINE 1: copy (SELECT * FROM TABLE WHERE month=6) TO '...

Does anyone know what can be wrong or give me a tip about?

Asked By: Raúl Casado

||

Source

Answer 1

COPY is a psql command (client based) and therefore not a valid SQL command. Try the same simply using COPY (without the backslash).

If you want the output file directly at the client, you might wanna use the STDOUT of COPY, otherwise the it will be created at the database server, which is a luxury not everyone has.

Answered By: Jim Jones

Answer 2

The copy is not an SQL command, it is a command specific for the Postgres terminal client psql and cannot be used in this context.

Use copy_expert(sql, file, size=8192) instead, e.g.:

sql = "COPY (SELECT * FROM a_table WHERE month=6) TO STDOUT WITH CSV DELIMITER ';'"
with open("/mnt/results/month/table.csv", "w") as file:
    cur.copy_expert(sql, file)

Read more about the function in the documentation.

Answered By: klin

Answer 3

Yes, all statements are correct related to COPY as SQL command.
If you want to try the same as you stated in the question then you can try it as a shell command in python script.

Eg:

import os
      
cmd1 = " Your SQL to csv Command"           
os.system(cmd1)

Answered By: aditya Mehta

Answer 4

You can use this syntax:

query = """ select * from instalacje WHERE date > '2022-02-20'"""

outputquery = "COPY ({0}) TO STDOUT WITH CSV HEADER".format(query)

with open("C:/1/Wojciech_CCC.csv", "w") as f:
    cur.copy_expert(outputquery, f)

Answered By: Wojciech Moszczyński

Exporting a PostgreSQL query to a csv file using Python

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