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  a b c ÁÐÃû
  1 2 t
  2 3 t
  4 3 r
  4 5 r
  1 2 w
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SQL code:
select count(distinct c) from tb

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select 
  count(distinct c) as cnt 
from tb

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ÒýÓÃ

SQL code
--> ²âÊÔÊý¾Ý£º[tb]
if object_id('[tb]') is not null drop table [tb]
go
create table [tb]([a] int,[b] int,[c] varchar(1),[ÁÐÃû] sql_variant)
insert [tb]
select 1,2,'t',null union all
select 2,¡­¡­

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