SQL，计入多列然后分组

Question

我试图计算多个列然后分组总和，其中相同的数据出现在任何列中

Source data table:

P1  P2  P3
-----------
a   b   
a   a   a
b   c   
a   b   b
b   a

我想要它显示这样的东西：

Desired query output:

     Total
   -------------
a |    6
b |    5
c |    1

Answer 1

您可以使用联合查询

SELECT x.f1,Count(x.f1) FROM
(SELECT p1 As F1 FROM table
 UNION ALL
 SELECT p2 As F1 FROM table
 UNION ALL
 SELECT p3 As F1 FROM table) x
GROUP BY x.f1

Answer 2

您可以将子查询和外部查询中的union all记录合并， count每个值。

SELECT b.a, COUNT(b.a)
FROM
    (
        SELECT P1 a
        FROM tableName
        UNION ALL
        SELECT P2 a
        FROM tableName
        UNION ALL
        SELECT P3 a
        FROM tableName
    ) b
GROUP BY b.a