Select most recent monthly anniversary day from a unix timestamp - mysql

Question

I have an app that inserts a Unix timestamp on registration. What I'd like to do, is calculate usage details for the month since the last monthly anniversary day. So I would need a unix timestamp of what the most recent anniversary day would be.
For example, if a registration is submitted on January 5, the customer's anniversary day is the 5th. So to check usage on February 15th, I need to retrieve all entries from the logs since Feb 5.
Getting the day of registration is easy:
SELECT DATE_FORMAT(FROM_UNIXTIME(created), '%d') FROM accounts
however, I'm lost finding the unix timestamp of the last anniversary date based on the registration day. How would I do that? To clarify, I'm looking to return all action_id created on or after the most recent anniversary date.
Tables:
accounts
+------------+------------+
| account_id | created |
+------------+------------+
| 1 | 1321838910 |
+------------+------------+
....
logs
+------------+------------+------------+
| account_id | action_id | created |
+------------+------------+------------+
| 1 | 233 | 1348249244 |
+------------+------------+------------+
| 1 | 263 | 1348257653 |
+------------+------------+------------+
....
Note: to keep things simple, I'm going to forgo figuring out what happens if an anniversary day is the 31st for example - that is, unless someone has a super ninja statement that takes those occurrences into account.

Answer 1

Not tested. See what you think. Logic is to:
Get the last day of the current month.
Add the account created day number of days to #1 result.
If current day is greater than created day, subtract 1 month from #2 result. Else subtract 2 months.
SELECT l.*
FROM accounts a
LEFT JOIN logs l
ON a.account_id = l.account_id
AND l.created >= UNIX_TIMESTAMP(
DATE_SUB(DATE_ADD(LAST_DAY(NOW()), INTERVAL DAY(FROM_UNIXTIME(a.created)) DAY),
INTERVAL IF(DAY(NOW()) > DAY(FROM_UNIXTIME(a.created)), 1, 2) MONTH));
Edit
I gave this some more thought and perhaps the query below will work regardless of when the anniversary date is. Assumption I made that if the anniversary day is not in a particular month then last day of the month should be taken. It's ugly but I put in some variables to make it more concise, there must be a nicer way. Anyway, I haven't tested but logic as follows.
If current day > anniversay day then just subtract the difference in days to get date.
else if the last day of the previous month is less than anniversary day then use the last day of previous month.
else subtract the day difference between anniversary day and last day of previous month from last date of previous month.
SELECT l.*
FROM accounts a
JOIN logs l
ON a.account_id = l.account_id
AND l.created >= UNIX_TIMESTAMP(
IF(#dNow := DAY(NOW()) >= #dCreated := DAY(FROM_UNIXTIME(a.created)),
DATE_SUB(NOW(), INTERVAL #dNow - #dCreated DAY),
IF(DAY(#endLastMonth := LAST_DAY(DATE_SUB(NOW(), INTERVAL 1 MONTH))) <= #dCreated,
#endLastMonth,
DATE_SUB(#endLastMonth, INTERVAL DAY(#endLastMonth) - #dCreated DAY))));

Answer 2

Perhaps this using order by desc to get most recent created date?
SELECT DATE_FORMAT(FROM_UNIXTIME(X.created), '%d')
FROM (
SELECT CREATED
FROM mytable
WHERE ACCOUNT_ID = ? -- customer id
AND DATE_DIFF(DATE_FORMAT(FROM_UNIXTIME(CREATED),'%Y-%m-%d'), NOW()) MOD 30 = 0
AND DATE_DIFF(DATE_FORMAT(FROM_UNIXTIME(CREATED),'%Y-%m-%d'), NOW()) / 30 = 1
ORDER BY CREATED DESC LIMIT 1)X;