In the last episode (Mar 16), Bob Cooper said:
> I am working with MySQL ver 5.1 on a Ubuntu Linux x86_64. I am new to
> both SQL and MySQL. I have been able to query out most of the data I
> need from my tables without any issues but his one has stumped me.
>
> I am trying to query data associated with specific dates. The dates
> are not sequential but somewhat sporadic. I would like to query out
> data/dates that are every 4 days from a starting date.
>
> 2006-4-17, 2006-4-21, etc.
>
> I have tried ADDDATE('2006-4-14',interval 4 day)<=Date_col
> but it give me only the next date 2006-4-21.
You could do it by converting to a daynumber (the number of days since
year 0) and doing modulo arithmetic:
WHERE TO_DAYS(date_col)%4 = TO_DAYS('2006-4-17')%4
http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html#function_to-days
--
Dan Nelson
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