zhwiki: talk exist but main not exist

SQL

SET @ns = 15;
USE zhwiki_p;
SELECT
	CONCAT("https://zh.wikipedia.org/w/index.php?title=",
case
	when talkpage.page_namespace = 0 then ""
	when talkpage.page_namespace = 1 then "Talk:"
	when talkpage.page_namespace = 2 then "User:"
	when talkpage.page_namespace = 3 then "User talk:"
	when talkpage.page_namespace = 4 then "Wikpeida:"
	when talkpage.page_namespace = 5 then "Wikpeida talk:"
	when talkpage.page_namespace = 6 then "File:"
	when talkpage.page_namespace = 7 then "File talk:"
	when talkpage.page_namespace = 8 then "Mediawiki:"
	when talkpage.page_namespace = 9 then "Mediawiki talk:"
	when talkpage.page_namespace = 10 then "Template:"
	when talkpage.page_namespace = 11 then "Template talk:"
	when talkpage.page_namespace = 12 then "Help:"
	when talkpage.page_namespace = 13 then "Help talk:"
	when talkpage.page_namespace = 14 then "Category:"
	when talkpage.page_namespace = 15 then "Category talk:"
	when talkpage.page_namespace = 100 then "Portal:"
	when talkpage.page_namespace = 101 then "Portal talk:"
	when talkpage.page_namespace = 118 then "Draft:"
	when talkpage.page_namespace = 119 then "Draft talk:"
	when talkpage.page_namespace = 828 then "Module:"
	when talkpage.page_namespace = 829 then "Module talk:"
end, ":", page.page_title, "&redirect=no ") AS "talk link",
	CONCAT(
case
	when talkpage.page_namespace = 0 then ""
	when talkpage.page_namespace = 1 then "Talk:"
	when talkpage.page_namespace = 2 then "User:"
	when talkpage.page_namespace = 3 then "User talk:"
	when talkpage.page_namespace = 4 then "Wikpeida:"
	when talkpage.page_namespace = 5 then "Wikpeida talk:"
	when talkpage.page_namespace = 6 then "File:"
	when talkpage.page_namespace = 7 then "File talk:"
	when talkpage.page_namespace = 8 then "Mediawiki:"
	when talkpage.page_namespace = 9 then "Mediawiki talk:"
	when talkpage.page_namespace = 10 then "Template:"
	when talkpage.page_namespace = 11 then "Template talk:"
	when talkpage.page_namespace = 12 then "Help:"
	when talkpage.page_namespace = 13 then "Help talk:"
	when talkpage.page_namespace = 14 then "Category:"
	when talkpage.page_namespace = 15 then "Category talk:"
	when talkpage.page_namespace = 100 then "Portal:"
	when talkpage.page_namespace = 101 then "Portal talk:"
	when talkpage.page_namespace = 118 then "Draft:"
	when talkpage.page_namespace = 119 then "Draft talk:"
	when talkpage.page_namespace = 828 then "Module:"
	when talkpage.page_namespace = 829 then "Module talk:"
end, ":", page.page_title) AS "talk"
FROM page AS talkpage
LEFT JOIN page AS mainpage ON talkpage.page_title = mainpage.page_title AND talkpage.page_namespace = mainpage.page_namespace+1
WHERE talkpage.page_namespace = (@ns)
		AND talkpage.page_title NOT LIKE "%/%"
		AND mainpage.page_title IS NULL
SQL

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