declare @t table( c varchar(10));
insert @t
select *
from
(
select 'A' as c union all
select 'B' union all
select 'B' union all
select null union all
select null
) t;
select count(*) from @t;
select count(c) from @t;
select count(distinct c) from @t;
select distinct c from @t;
测一下上面最后四条语句的执行结果：
Code
