查询以获得mysql中的平均值和不同值

Question

我在表格中有这样的数据：

================================
class | name   | study | average
================================
1       alfa     c#       70 
1       beta     c#       70
2       carlie   c#       80
2       delta    c#       80
1       alfa     php      80
1       beta     php      90
2       carlie   php      70
2       delta    php      80

我想要这样的结果：

===============================
study |   class    | avg class
      | 1   |   2  |
===============================
c#      70    80       75
php     85    75       80

那么如何在mysql中进行查询以获得这些结果呢？

请帮助我，我已多次尝试但未成功

由于

Answer 1

这应该对你有用，但是你必须添加一个新的＆＃34;类＆＃34;每个数字类号的行。

SELECT study,
    (SELECT AVG(average) FROM test t WHERE class='1' AND t.study = test.study) as 'class 1',
    (SELECT AVG(average) FROM test t WHERE class='2' AND t.study = test.study) as 'class 2',
    AVG(average)
FROM test
GROUP BY study

Fiddle.

Answer 2

试试这个：

SELECT
    study,
    AVG
    (
        CASE 
            WHEN class = 1 THEN average
            ELSE NULL
        END
    ) class_1_average,
    AVG
    (
        CASE 
            WHEN class = 2 THEN average
            ELSE NULL
        END
    ) class_2_average,
    AVG(average) avg_class
FROM mytable
GROUP BY study;