MySQL每月平均datediff

Question

I have for example following databse:

date1      | date2      | datediff
2016-11-02 | 2016-11-05 | 3
2016-11-08 | 2016-11-10 | 2
2016-11-01 | 2016-11-05 | 4
2016-11-09 | 2016-11-09 | 0
2016-11-15 | 2016-11-20 | 5

I get the datediff with following sql:

select 
datediff(date2, date1)
from table

Now I need the average datediff for each month, in this case for 2016-11: 2.8

Thanks in advance, Patrick.

Answer 1

you can use month(), AVG and group by

select year(date1), month(date1), avg(datediff(date2, date1))
from my_table 
group by year(date1), month(date1)
;

Answer 2

I think you can just use group by :

select year(date1), month(date1), AVG(datediff(date2, date1))
from table
group by year(date1), month(date1);

Answer 3

select AVG(datediff(date2, date1))
from table
group by year(date1), month(date1);

Answer 4

You can get the last day of the month for any date / time value with the LAST_DAY() function . (It sounds more apocalyptic than it is.) That's useful for grouping.

So, try

 SELECT LAST_DAY(date1) month_ending, AVG(DATEDIFF(date2,date1)) datediff
   FROM table
  GROUP BY LAST_DAY(date1)
  ORDER BY LAST_DAY(date1)

Answer 5

select avg(datediff(date2, date1))as difference
from table
group by year(date1),month(date1)