SQL
AخA
# based on https://en.wikipedia.org/wiki/Wikipedia:Database_reports/Self-categorized_categories/Configuration
SELECT
p1.page_title, p2.page_title
FROM
page as p1,
page as p2,
categorylinks as cl1,
categorylinks as cl2
WHERE
cl1.cl_to = p2.page_title
AND p2.page_namespace = 14
AND p2.page_id = cl2.cl_from
AND cl2.cl_to = p1.page_title
AND p1.page_namespace = 14
AND p1.page_id = cl1.cl_from
AND p1.page_id < p2.page_id;
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