After applying the Magento patch SUPEE-6788, I find that the tables
permission_variable are not created in the database. How should I start investigate this problem? (The Magento version is 126.96.36.199)
Answered in comments.
You will need to clear the cache a reload the homepage in order for magento's update scripts to be called. Alternatively you can download N98-magerun and run the
sys:setup:run command to run the updates.