How Can I Get a Comma-Separated List of Values in MySQL Query Results?

Generating Comma-Separated Lists in MySQL Query Results

Many database users require comma-separated lists from their MySQL queries. While MySQL doesn't directly support this, the GROUP_CONCAT function offers a simple solution.

The Problem

Imagine a query retrieving publication data and associated site names:

<code class="language-sql">SELECT p.id, p.name, 
       (SELECT name 
          FROM sites s 
         WHERE s.id = p.site_id) AS site_list
  FROM publications p;</code>

This returns a "site_list" column with only one site name per publication. We need a comma-separated list instead.

The Solution: GROUP_CONCAT

The GROUP_CONCAT function concatenates values from a column. Here's the improved query:

<code class="language-sql">SELECT p.id, p.name, GROUP_CONCAT(s.name) AS site_list
FROM sites s
INNER JOIN publications p ON s.id = p.site_id
GROUP BY p.id, p.name;</code>

This uses an INNER JOIN to link "sites" and "publications" tables, ensuring correct site-publication associations. GROUP_CONCAT(s.name) concatenates site names, and GROUP BY p.id, p.name groups the results by publication ID and name, creating the desired comma-separated list in the "site_list" column. This efficiently provides the required output.

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