Guidance For Selecting Cdbcachedependency

Yii 1.1 General Discussion
1

As an CDbCacheDependency i use:


select unix_timestamp(MAX(update_date)),count(*) from advert

or


select unix_timestamp(MAX(update_date))+count(*)  from advert

which of these are beter?

My intention is if count of records or update_date were changed the cache will be expired.