Appends “ (duplicate)” to any duplicate tags within a Craft CMS database. Assumes table prefix is `craft_`.

query.sql

UPDATE craft_content
SET craft_content.title = CONCAT(craft_content.title, ' (duplicate)')
WHERE craft_content.elementId IN (
  SELECT tmp.elementId
  FROM (
    SELECT *
    FROM craft_content
  ) AS tmp
  JOIN craft_tags ON craft_tags.id = tmp.elementId
  GROUP BY tmp.title
  HAVING COUNT(*) > 1
)

Needs to be limited to specific tag groups via a second JOIN within the sub-query.