SELECT page_title, page_len, CONCAT('https://enwp.org/Talk:', page_title) as URL

FROM page AS talk

WHERE page_namespace = 1

  AND page_title NOT IN (

                            SELECT main.page_title

                            FROM page AS main

                            WHERE page_namespace = 0

                              AND main.page_title = SUBSTRING_INDEX(talk.page_title, '/', 1)

                        )

LIMIT 50;