Query results are different between piwik and DB

Hi,

We are trying to get the page views using an SQL query and compare it to Piwik results. Consistently, we are finding that Piwik has lower values than our queries. Our query is as follows:

Select piwik_log_link_visit_action
Where idsite = 2
AND idaction_event_action is null

This always yields a higher result than what we see in Piwik. Is there any filtering that happens in the front end that causes this difference? Or is there something we are missing here?

Thank you for your help,
Ihab