题解 | #统计所有课程参加培训人次#

select sum(
    case 
    when course in ('course1','course2','course3') then 1 
    when course in ("course1,course2","course1,course3","course2,course3") then 2 
    when course in ('course1,course2,course3') then 3
    else 0
    end 
 ) staff_nums
from cultivate_tb;