use enwiki_p;

SELECT 

  database() AS dbname,

  wp.page_title AS Title,

  pp_value,

  el_to

FROM page AS wp

JOIN externallinks ON el_from = wp.page_id

LEFT JOIN page_props AS pp

    ON pp.pp_page = wp.page_id AND pp.pp_propname = 'wikibase_item'

LEFT JOIN wikidatawiki_p.page AS wdp

    ON wdp.page_title = pp.pp_value AND wdp.page_namespace = 0

LEFT JOIN wikidatawiki_p.pagelinks AS wdpl

  ON wdpl.pl_from = wdp.page_id AND wdpl.pl_namespace = 120 AND wdpl.pl_title = 'P1447'

WHERE wp.page_namespace = 0

AND   el_to    LIKE 'http://www.sports-reference.com/olympics/athletes/%'

AND   wdpl.pl_from IS NULL;