Question

我有一个包含以下各列的收集表：

id (INT)
col1 (VARCHAR)
col2 (VARCHAR)
value (INT)

我想分别通过col1和col2计算平均值，以获得这样的响应：

{
    averageByCol1: {col1Value1: 23, col1Value2: 44},
    averageByCol2: {col2Value1: 33, col2Value2: 91}
}

试图在GROUP BY中使用多个列，但这将合并这些列：

SELECT
CONCAT(col1, col2, AVG(value))
FROM table1
GROUP BY col1, col2

也尝试了子查询，但它给了我Subquery returns more than 1 row错误：

SELECT
    (SELECT
    CONCAT(col1, AVG(value))
    FROM table1
    GROUP BY col1) AS col1Averages,
    (SELECT
    CONCAT(col2, AVG(value))
    FROM table1
    GROUP BY col2) AS col2Averages;

使用Mysql v5.5。

使用示例数据进行编辑：

id  col1    col2    value
1   v1      b1      34
2   v2      b1      65
3   v1      b1      87
4   v1      b2      78
5   v2      b2      78
6   v1      b2      12

分别由v1，v2，b1和b2求value的平均值。

Answer 1

对要计算平均值的每一列使用UNION

SELECT col1 as col_key, avg(value) as average
FROM test
GROUP BY col1
UNION
SELECT col2, avg(value)
FROM test
GROUP BY col2

Answer 2

这将起作用：

  select avg(value),col1 from Table1 group by col1
  union all
  select avg(value),col2 from Table1 group by col2

sql小提琴：http://sqlfiddle.com/#!9/c1f111/5/0

Answer 3

如果您要查询2个单独的结果：

SELECT col1, AVG(value) AS average1
from table1
GROUP BY col1
ORDER BY col1

和

SELECT col2, AVG(value) AS average2
from table1
GROUP BY col2
ORDER BY col2

多列平均值分别

3 个答案: