GROUP BY 对列、聚合和转换结果

Question

我有下表：

date       | data_type | data_value
01-01-2023 |  max      |    4
02-01-2023 |  min      |    7
03-01-2023 |  avg      |    54
04-01-2023 |  max      |    8
05-01-2023 |  min      |    98
06-01-2023 |  avg      |    23
01-02-2023 |  max      |    65
02-02-2023 |  min      |    2
03-02-2023 |  avg      |    45
04-02-2023 |  max      |    22
05-02-2023 |  min      |    56
06-02-2023 |  avg      |    65
01-03-2023 |  max      |    7
02-03-2023 |  min      |    5
03-03-2023 |  avg      |    23
04-03-2023 |  max      |    65
05-03-2023 |  min      |    51
06-03-2023 |  avg      |    33

从下表中，我需要按当前月份分组，并从中获取其数据类型为“max”的最大值，类型为“min”的较小值，最后是类型“avg”的平均值，如下：

mounth | max | min |  avg
1      |  8  |  7  |  38,5
2      |  65 |  2  |  55
3      |  65 |  5  |  28

---

因此我想问你哪个是性能最好的 SQL 查询来解决请求。

谢谢大家

Answer 1

使用条件聚合如下：

select year(date_) as 'yaer',
       month(date_) as 'month',
       min(case when data_type = 'min' then data_value end) as 'min',
       max(case when data_type = 'max' then data_value end) as 'max',
       avg(case when data_type = 'avg' then data_value end) as 'avg'
from tbl
group by year(date_), month(date_)

或者，如果您想汇总特定年份：

select month(date_) as 'month',
       min(case when data_type = 'min' then data_value end) as 'min',
       max(case when data_type = 'max' then data_value end) as 'max',
       avg(case when data_type = 'avg' then data_value end) as 'avg'
from tbl
where year(date_) = 2023
group by month(date_)

查看演示。