Setting subscription dates in MySQL

Question

I'm dealing with a website where people can subscribe to certain things for virtual money. I need to put the dates at which subscriptions end in the database. My table has a field "expiration" for that, which is a DATE.

When the user extends his subscription, I need to add 1 month to this date. However, if the subscription has already expired, I want to set "expiration" to 1 month from now, not to 1 month from when the subscription expired.

I've tried:

UPDATE shop_user_rights SET expiration = ADDDATE(MAX(expiration, CURDATE()), INTERVAL 1 MONTH);

and

UPDATE shop_user_rights SET expiration = FROM_UNIXTIME(
 MIN(
  UNIX_TIMESTAMP(expiration),
  UNIX_TIMESTAMP(CURDATE())
 )
),
expiration = ADDDATE(expiration, INTERVAL 1 MONTH);

But both give syntax errors. Is there a way to do this in 1 query, or do I have to use some SELECT queries beforehand?

Answer 1

The MIN() and MAX() functions are for grouping: you want LEAST() and GREATEST() instead.