如何在mysql中获得一个月的平均值？

Question

i have day, month, year, value columns in one table, here i need to get every week average value in one month. how to get that. please help me regarding this.

select avg(value) from table group by month 

gives month average.

select avg(value) from table group by day

gives day average. but how to get week average from month field.

Answer 1

You can't "get weeks from a month" as one is not a subset of the other.
The number of days (and hence weeks) in 1 month varies from month to month and only in non-leap years - and in February only - are there exactly 4 weeks in a month.

You should use the original date field and use a date function to limit/group the data by week.
get the week in mySQL with
WEEK(timestamp)
or
YEARWEEK(timestamp)
or
WEEKOFYEAR(NOW())
or
DATE_FORMAT($yourDate, \\'%X %V\\') as week

Answer 2

There might be a better way, but my first thought is to write a query that calculates the week of the year for each day and groups them. http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_weekofyear

Something like:

SELECT avg(value) FROM table GROUP BY WEEKOFYEAR(CONCAT(year, '-', month, '-', day))