How to Efficiently Export PL/pgSQL Query Results to a CSV File in PostgreSQL?

Export PL/pgSQL output to CSV file in PostgreSQL

Introduction

Exporting data from PostgreSQL to CSV file is a common task in data analysis and further processing. This article explores two ways to achieve this using PL/pgSQL procedures:

Server side method

This method utilizes PostgreSQL’s built-in COPY command. It allows you to write SQL result sets directly to a file on the server. Example:

<code>COPY (SELECT * FROM foo) TO '/tmp/test.csv' WITH CSV DELIMITER ',' HEADER;</code>

Advantages:

• Highly efficient for exporting large data
• Run entirely on the server, minimizing client-server overhead

Disadvantages:

• Super user rights required
• Can only write to files on the server

Client method

You can use COPY TO STDOUT to retrieve the data and handle the file writing in the client application instead of using COPY on the server. Example in psql:

<code>\copy (SELECT * FROM foo) TO '/tmp/test.csv' WITH CSV DELIMITER ',' HEADER</code>

Advantages:

• No superuser rights required
• Allow access to files on client

Disadvantages:

• May be slower than server side approach
• Requires additional processing in client application

Safety Precautions

If you choose a server-side approach, be sure to implement appropriate security measures, such as:

• Use the SECURITY DEFINER option to create functions to enforce specific file and table access permissions on users.
• Double-check file permissions and make sure the server cannot access sensitive data.

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