Redshift count(*) VS count(col)

with tmp as (

select 1 as a, 2 as b

union all

select 1 as a, 2 as b

union all

select 1 as a, null as b

)

select * from tmp;

with tmp as (

select 1 as a, 2 as b

union all

select 1 as a, 2 as b

union all

select 1 as a, null as b

)

select count(*), count(b) from tmp;

各列在行上的并集