(一)、根据teacher_no统计星期的上课数-- 解法一
SELECT
t1.teacher_no,
(CASE WEEK WHEN '1' THEN keshu ELSE 0 END ) 礼拜一,
(CASE WEEK WHEN '2' THEN keshu ELSE 0 END ) 礼拜二,
(CASE WEEK WHEN '3'