题解 | 统计所有课程参加培训人次

select 
(sum(if(mid(course,1,7)='course1',1,0)) 
+ sum(if(course like '%2%',1,0)) 
+ sum(if(course like '%3%',1,0))) staff_nums 
from cultivate_tb

# with t1 as(
#     select count(staff_id) staff_nums from cultivate_tb
#     where mid(course,1,7) = 'course1'
# ),
# t2 as(
#     select count(staff_id) staff_nums from cultivate_tb
#     where course like '%course2%'
# ),
# t3 as(
#     select count(staff_id) staff_nums from cultivate_tb
#     where course like '%course3%'
# )
# select t1.staff_nums + t2.staff_nums + t3.staff_nums staff_nums from t1,t2,t3