SELECT article.page_len, article.page_title, article.page_id

FROM page talk

INNER JOIN page article ON

  talk.page_title = article.page_title

INNER JOIN categorylinks ON

  cl_from = talk.page_id

WHERE

  talk.page_namespace = 1 AND

  article.page_namespace = 0 AND

  cl_to IN ("FA-Class_mathematics_articles",

            "GA-Class_mathematics_articles",

            "A-Class_mathematics_articles",

            "B-Class_mathematics_articles",

            "C-Class_mathematics_articles",

            "Start-Class_mathematics_articles",

            "Stub-Class_mathematics_articles",

            "Unassessed_mathematics_articles");