Podrías obtener una lista de temas que tengan solo una etiqueta específica mediante una consulta del Explorador de Datos. Algo como esto podría funcionar para ti:
--[params]
-- string :tag_name
with tagged_topics AS (
SELECT
topic_id
FROM topic_tags
JOIN tags
ON tags.id = topic_tags.tag_id
WHERE tags.name = :tag_name
),
counts AS (
SELECT
COUNT(id) AS tag_count,
tagged_topics.topic_id
FROM topic_tags
JOIN tagged_topics
ON tagged_topics.topic_id = topic_tags.topic_id
GROUP BY tagged_topics.topic_id
)
SELECT
c.topic_id
FROM counts c
JOIN topics t
ON t.id = c.topic_id
WHERE t.deleted_at IS NULL
AND t.archetype = 'regular'
AND c.tag_count = 1