Unfortunately, if you don't have advanced knowledge of how the database tables are connected to one another, you will cause a lot of errors directly editing data in the database. You're better off writing code to perform you updates and using the API to handle these mass updates.
Regarding your current problem at hand.
Do you have versioning enabled?
Do you have workflow enabled?
If you answered yes to either of those questions, this is your underlying problem. Based on your question, you're updating the data directly in the page type's table. Unfortunately, with versioning and workflow, you need to update XML in another connecting table and NOT the page type's table.
So aside from telling you how to update XML in SQL, I'll provide some workarounds to get this working.
- First, make sure all your pages are checked in.
- Make sure all your pages are properly published in workflow.
- Remove all pages from workflow (done in the workflow app).
- Turn off check-in/out in your workflow.
- Manually run the t-sql update on your pages.
- Restart your web app's application pool.
- Navigate to your website and look for new content.
- Renable workflow and versioning.