我有一个Statistics表，如下所示
parent key value date
MASTER maths 400 2016-10-12
MASTER maths 200 2016-10-20
MASTER maths 350 2016-10-23
MASTER passed 20% 2016-10-25
MASTER passed 40% 2016-10-27
MASTER passed 30% 2016-10-28
MASTER maths 500 2016-11-12
MASTER maths 250 2016-11-20
MASTER maths 600 2016-11-23
MASTER passed 55% 2016-11-25
MASTER passed 75% 2016-11-27
MASTER maths 500 2016-12-12
MASTER maths 250 2016-12-20
MASTER maths 600 2016-12-23
MASTER passed 70% 2016-12-25
MASTER passed 65% 2016-12-26
MASTER passed 45% 2016-12-27
MASTER maths 500 2017-01-12
MASTER maths 450 2017-01-20
MASTER maths 770 2017-01-23
MASTER passed 87% 2017-01-25
MASTER passed 54% 2017-01-27
MASTER maths 900 2017-02-12
MASTER maths 250 2017-02-20
MASTER maths 500 2017-02-23
MASTER passed 67% 2017-02-25
MASTER passed 45% 2017-02-27
我要求使用mysql
调出如下所示的输出maths passed date
950 30% 2016-10
1350 65% 2016-11
1350 60% 2016-12
1720 70.5% 2017-01
1650 56% 2017-02
我写的我的查询在下面给出
SELECT SUM(CASE WHEN key = 'maths' THEN value ELSE 0 END) AS maths,
SUM(CASE WHEN key = 'passed' THEN value ELSE 0 END) AS passed
FROM Statistics
WHERE parent = 'MASTER' GROUP BY MONTH(date) ORDER BY date ASC
但我是通过而不是平均值的总和，也就是说如果我得到 20％，40％和 30％那么我应该得到平均值为 30％，但对于我上面的查询，我得到 90％。 ％也会在结果
中消失任何人都可以帮助我
答案 0 :(得分：1)
使用子查询：
要计算AVG，首先需要知道有多少行已经“传递”了值。
（检查here。）
select yr as `year`, mt as `month`,
sum(val_maths) as `math`,
concat(cast((sum(val_passed) / sum(count_passed)) as char(50)), '%') as `passed`
from (
select ky, year(dt) as yr, month(dt) as mt,
if (ky = 'maths', replace(val,'%',''), 0) val_maths,
if (ky = 'passed', replace(val,'%',''), 0) val_passed,
if (ky = 'passed', 1, 0) as count_passed
from foot
) tv
group by yr, mt
;
| year | month | maths | passed |
|-------|-------|--------|--------|
| 2016 | 10 | 950 | 30% |
| 2016 | 11 | 1350 | 65% |
| 2016 | 12 | 1350 | 60% |
| 2017 | 1 | 1720 | 70.5% |
| 2017 | 2 | 1650 | 56% |
答案 1 :(得分：1)
您必须对AVG使用average聚合函数。
更改：
SUM(CASE WHEN key = 'passed' THEN value ELSE 0 END) AS passed
以：
AVG(CASE WHEN key = 'passed' THEN value ELSE 0 END) AS passed
％符号已删除
当运算符与不同类型的操作数一起使用时，会发生类型转换以使操作数兼容。某些转换是隐式发生的。例如，MySQL会根据需要自动将数字转换为字符串，反之亦然。
要显示%符号，您可以将其与结果联系
在您的查询中进行更改后，可能会帮助您获得所需的结果。
mysql> SELECT DATE_FORMAT( `date`, '%Y-%m' ) AS `month`
-> , SUM( CASE `key` WHEN 'maths' THEN `value` ELSE NULL END ) AS `maths`
-> -- , SUM( CASE `key` WHEN 'passed' THEN `value` ELSE NULL END ) AS `passed`
-> , CONCAT( ROUND( AVG( CASE `key` WHEN 'passed' THEN `value` ELSE NULL END ), 2 ), '%' ) AS `passedAvg`
-> FROM Statistics
-> WHERE parent = 'MASTER'
-> GROUP BY MONTH(`date`)
-> ORDER BY `date` ASC;
结果可以是这样的：
+---------+-------+-----------+
| month | maths | passedAvg |
+---------+-------+-----------+
| 2016-10 | 950 | 30.00% |
| 2016-11 | 1350 | 65.00% |
| 2016-12 | 1350 | 60.00% |
| 2017-01 | 1720 | 70.50% |
| 2017-02 | 1650 | 56.00% |
+---------+-------+-----------+
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