text: 
  SELECT COUNT(DISTINCT account.display_name)
  FROM tag t1,
       site s1,
       question q1,
       answer a1,
       tag_question tq1,
       so_user u1,
       account
  WHERE -- answerers posted at least 1 yr after the question was asked
  s1.site_name='math'
    AND t1.name = 'algebra-precalculus'
    AND t1.site_id = s1.site_id
    AND q1.site_id = s1.site_id
    AND tq1.site_id = s1.site_id
    AND tq1.question_id = q1.id
    AND tq1.tag_id = t1.id
    AND a1.site_id = q1.site_id
    AND a1.question_id = q1.id
    AND a1.owner_user_id = u1.id
    AND a1.site_id = u1.site_id
    AND a1.creation_date >= q1.creation_date + INTERVAL '1' YEAR
    AND -- to get the display name
  account.id = u1.account_id;