oracle 统计字段空值数

select sum( case when a is nul then 1 end),
sum( case when b is nul then 1 end),
sum( case when c is nul then 1 end)
from table1 ;

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select
'a' 字段，
sum( case when a is nul then 1 end)
from table1
union all
select
'b' 字段，
sum( case when b is nul then 1 end)
from table1
select
'c' 字段，
sum( case when c is nul then 1 end)
from table1 ;