Hive count(*) 会统计NULL，count(字段名)不统计NULL

Posted 2021-06-28 二十六画生的博客

select count(*) 
from 
(
select 1  as c1
union all
select null as c1
) -- 2  , count(*) 包含null值


select count(c1) 
from 
(
select 1  as c1
union all
select null as c1
) -- 1  , count(c1) 不包含null值


select count(case when 1=1 then 1 else 0 end) ; -- 1

select count(case when 1<>1 then 1 else null end) -- 0 

select count(0)  -- 1

select count(null)  -- 0

select
type,
count(case when status = 3 then id else null end) as cnt
from (
select 
1 as id ,
2 as status,
1 as type
union ALL
select 
3 as id ,
4 as status,
1 as type
union ALL
select 
2 as id ,
3 as status,
2 as type
union ALL
select 
4 as id ,
3 as status,
2 as type
) t1
group by type
order by type ;

---------- 

select
type,
count(case when status = 3 then id else 0 end) as cnt
from (
select 
1 as id ,
2 as status,
1 as type
union ALL
select 
3 as id ,
4 as status,
1 as type
union ALL
select 
2 as id ,
3 as status,
2 as type
union ALL
select 
4 as id ,
3 as status,
2 as type
) t1
group by type
order by type ;

 end