MySql 平均日期差

Question

I have a problem and I don't know if it is possible to solve it. Namely, I have a MySQL database with two columns: id and date. How can I formulate a query that will calculate the average difference of all dates? For example, between 1 and 2 the date is 14 days, between 2 and 3 is 12 days so the average will be 13 days.

Answer 1

The average is just the largest value minus the smallest divided by one less than the number of values. So:

select datediff(max(date), min(date)) / nullif(count(*) - 1, 0)
from t;

You can easily see this if you look at the numbers:

 1
 5       . . . 4
 10      . . . 5
 19      . . . 9

The average difference is (4 + 5 + 9) / 3 = 6.

It is not a coincidence that (19 - 1) / 3 = 6 as well. It is a mathematical certainty.

You can easily see this. The average difference is:

( (5 - 1) + (10 - 5) + (19 - 10) ) / 3

You can rearrange this:

( -1 + (5 - 5) + (10 - 10) + 19 ) / 3

which is:

( 19 - 1 ) / 3

Answer 2

Hope this will help

SELECT  AVG(DATEDIFF(Date, NextDate)) 
    FROM    (   SELECT  
                        Date,
                        (   SELECT  MIN(Date) 
                            FROM    YourTable T2
                            WHERE   T2.Date > T1.Date
                        ) AS NextDate
                FROM    YourTable T1
            ) AS T

*use your table name for YourTable

this works when the there are non overlapping date ranges between two dates in rows. If there are ranges of 0 as well then use >= instead of >