sql计数3列中的值

Question

当可能的值可以在0到3列的任何值时，如何计算所有值。我想把所有的a，b，s，c＆s，d＆＃39>加起来

COL1     COL2     COL3
a
b
b         a
a         c        b
a         b
c         a   
d         a        c
c         d      

Answer 1

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

Answer 2

您可以使用UNPIVOT：

SELECT t.Val, COUNT(*) AS cnt
FROM (
  SELECT Col1, Col2, Col3
  FROM mytable
  UNPIVOT (
     Val FOR Col IN ("Col1", "Col2", "Col3"))) t
GROU BY t.Val