select col,count(*)
from(select col1 as col from tb
     union all 
     select col2 from tb
     unioin all 
     select col3 from tb) as t
group by col

------解决方案--------------------

SQL code


if object_id('[table4]') is not null drop table [table3]
create table [table4]([col1] VARCHAR(32),[col2] VARCHAR(32),[col3] VARCHAR(32))
insert [table4]
select   'a ','a ','b' union all
select   'c ','b', 'a'   union all
select   'b','b' ,'b'

SELECT col,sum(1) value FROM(
SELECT col1 AS col FROM table4
UNION ALL
SELECT col2 AS col FROM table4
UNION ALL
SELECT col3 AS col FROM table4) tb
GROUP BY col

col  value
---- -----
a        3
b        5
c        1