SQL
Aggregating String Values with GROUP_CONCAT or STRING_AGG
Combine multiple string values from related rows into a single, comma-separated string within a grouped result. Ideal for listing tags, categories, or associated items.
-- MySQL / MariaDB Syntax
SELECT
p.PostID,
p.Title,
GROUP_CONCAT(t.TagName ORDER BY t.TagName ASC SEPARATOR ', ') AS Tags
FROM
Posts p
JOIN
PostTags pt ON p.PostID = pt.PostID
JOIN
Tags t ON pt.TagID = t.TagID
GROUP BY
p.PostID, p.Title;
-- PostgreSQL Syntax
SELECT
p.PostID,
p.Title,
STRING_AGG(t.TagName, ', ' ORDER BY t.TagName ASC) AS Tags
FROM
Posts p
JOIN
PostTags pt ON p.PostID = pt.PostID
JOIN
Tags t ON pt.TagID = t.TagID
GROUP BY
p.PostID, p.Title;
How it works: String aggregation functions like `GROUP_CONCAT` (MySQL) and `STRING_AGG` (PostgreSQL) are used to concatenate strings from multiple rows within a group into a single string. This snippet demonstrates how to retrieve all tags associated with a blog post, combining them into a single, comma-separated string in the `Tags` column for each post, simplifying data retrieval for many-to-many relationships.