USE enwiki_p;

SELECT unspaced_page_title, child_titles

FROM (

SELECT 

  unspaced_page_title,

  COUNT(page_title) AS num_child_titles,

  GROUP_CONCAT(page_title SEPARATOR "; ") AS child_titles

FROM (

  SELECT

    page_title,

    REPLACE(page_title, "_", "") AS unspaced_page_title

  FROM page

  WHERE

    page_namespace = 10

) AS subquery1

GROUP BY unspaced_page_title

) AS subquery2

WHERE num_child_titles > 1