题解 | 统计所有课程参加培训人次
SELECT SUM(num) staff_nums
FROM
(SELECT
staff_id,
CASE
WHEN LENGTH(course) = 15 THEN 2
WHEN LENGTH(course) = 7 THEN 1
WHEN LENGTH(course) = 23 THEN 3
ELSE 0 END num
FROM cultivate_tb ct) t_1