题解 | 大小写混乱时的筛选统计

SELECT
  MAX( tag ) tag,
  MAX( answer_cnt ) answer_cnt 
FROM
  (
  SELECT
    MAX( er.exam_id ) exam_id,
    ei.tag tag,
    COUNT( 1 ) answer_cnt 
  FROM
    exam_record er
    INNER JOIN examination_info ei ON er.exam_id = ei.exam_id 
  GROUP BY
    tag 
  ) t 
GROUP BY
  UPPER( tag ) 
HAVING
  COUNT( exam_id )> 1 
ORDER BY
  answer_cnt DESC