sum(case when then)(判断男女生的个数)

判断类似一个班级的男生和女生的人数，用sum (cese when then )

select count(er.execute_result),
sum(case er.execute_result when 1 then 1 else 0 end) completed,
sum(case er.execute_result when 0 then 1 else 0 end) notcompleted
from taw_wp_execute_result er ;

select
(case when er.execute_result>0 then 'a'
else 'b'
end
)
from taw_wp_execute_result er ;