题解 | 统计所有课程参加培训人次

select
sum(t1.c1_nums)+ sum(t1.c2_nums)+ sum(t1.c3_nums) as staff_nums
from
(select
staff_id,
case
    when instr(c.course,'1')!=0 then 1 else 0 end as c1_nums,
case
    when instr(c.course,'2')!=0 then 1 else 0 end as c2_nums,
case
    when instr(c.course,'3')!=0 then 1 else 0 end as c3_nums
from cultivate_tb c
where c.course is not null) t1;