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

Exporting PL/pgSQL Results to CSV in PostgreSQL: Two Methods

PostgreSQL's PL/pgSQL procedural language allows for powerful database extensions. This guide details two methods for saving PL/pgSQL query results to a CSV file.

Method 1: Server-Side Export using COPY

The most efficient server-side approach utilizes PostgreSQL's COPY command. A command like this:

<code class="language-sql">COPY (SELECT * FROM foo) TO '/tmp/test.csv' WITH CSV DELIMITER ',' HEADER;</code>

exports data from the "foo" table to a CSV file on the server. Crucially, this requires appropriate server-side permissions. Best practice involves creating a dedicated function with the SECURITY DEFINER option to manage these permissions securely.

Method 2: Client-Side Export using COPY TO STDOUT

Alternatively, you can handle CSV export on the client-side using the COPY TO STDOUT command within the psql command-line client. The copy meta-command facilitates this:

<code class="language-sql">\copy (SELECT * FROM foo) TO '/tmp/test.csv' WITH CSV DELIMITER ',' HEADER</code>

Note that copy is a meta-command, not a standard SQL command, so a terminating semicolon (;) is unnecessary.

Security Considerations (Server-Side):

The server-side approach necessitates careful security planning:

• Restricted File System Access: Limit the function's file system access to only the necessary directories.
• Controlled Database Access: Restrict database access to only the required tables.
• Robust Input Validation: Implement thorough checks to prevent malicious inputs.

Considerations for Client-Side Approach:

When using the client-side method:

• Language Compatibility: Ensure your application's programming language supports the necessary file handling functions.
• Performance for Large Datasets: For large datasets, the performance of built-in functions like PHP's pg_copy_from and pg_copy_to might be suboptimal. Consider alternative, more efficient methods.

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