Commons file pages linked from a page - very slow with extra join

Fork of Most common categories for Commons file pages linked from a page by Jheald

This query is marked as a draft This query has been published by Jheald.

Query becomes catastrophically slow when the 'fp' page table join is added -- because there is apparently no index on the "page_title" field of the page table.

Solution: see https://quarry.wmflabs.org/query/34008 -- page-namespace also needs to be specified in join

SQL

use commonswiki_p;

SELECT DISTINCT pl.pl_title #, GROUP_CONCAT(cl.cl_to SEPARATOR ' / ') AS cats

FROM page AS p0
JOIN pagelinks AS pl ON pl.pl_from=p0.page_id AND pl.pl_from_namespace=p0.page_namespace AND pl.pl_namespace=6
# JOIN page AS fp ON fp.page_title = pl.pl_title
# JOIN categorylinks AS cl ON cl.cl_from = fp.page_id

WHERE p0.page_title='British_Library/MC_maps_batch_01_(GB_counties)' AND p0.page_namespace=4

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