如何计算 Postgresql 中具有相同时间戳的值的平均值？

Question

i have the following table:

date	value	Average
2021-04-07 18:00:00	5
2021-04-07 18:00:00	10
2021-04-07 18:02:00	5
2021-04-07 18:02:00	4
2021-04-07 18:03:00	5
2021-04-07 18:03:00	8

And i want to know how could i calculate the average of values with the same timestamp, like this:

date	value	Average
2021-04-07 18:00:00	5	7,5
2021-04-07 18:00:00	10	7,5
2021-04-07 18:02:00	5	4,5
2021-04-07 18:02:00	4	4,5
2021-04-07 18:03:00	5	6,5
2021-04-07 18:03:00	8	6,5

I'm also wondering if it would be easier to calculate the average on a separate table so they won't repeat because there is more than one row with the same timestamp. Hope someone can help me with this, thanks in advance.

Answer 1

In an internal select, obtain the avg with the group by date . Then join the records whose date is equal to the internal select date .

SELECT t1.date,t2.value,t1.average 
FROM
 (SELECT date,AVG(Cast(value as Float)) as average
 FROM yourTable
 GROUP BY date) t1 JOIN yourTable t2 ON t1.date = t2.date

result: dbfiddle

Answer 2

SELECT CAST(date AS DATE) as DateField, AVG(value) as avg_value
FROM MyTable
GROUP BY CAST(date AS DATE)

Answer 3

A simple query:

SELECT date, AVG(value) as avg_value FROM MyTable GROUP BY date

Answer 4

Use a window function:

select t.*,
       avg(value) over (partition by date) as timestamp_average
from t;