In the last episode (Mar 18), Jim Ginn said:
> > 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
>
> I've used the TO_DAYS on a SELECT statement ie:
>
> SELECT * FROM properties WHERE
> (TO_DAYS(NOW()) - TO_DAYS(CreationDate) = 1) ORDER BY id DESC
>
> however it didn't seem to take advantage or use the index on that field
> (ie. CreationDate) ...
Right; mysql needs CreationDate all by itself on one side of a
comparison operator to be able to use an index. In your case, try
WHERE CreationDate = CURDATE() - INTERVAL 1 DAY
, assuming CreationDate is a 'date' field type. If it's a datetime,
you'll need to use a BETWEEN operator and cover the time range from
midnight to midnight on your target day.
--
Dan Nelson
[EMAIL PROTECTED]
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