I am looking for studies about statistics on database usage. These are the questions I am looking the answer for:

1. What is the average amount of tables in an typical database?
2. What is the average size of a record in a table?
3. What is the typical frequency of INSERTs, SELECTs, UPDATEs and DELETEs ?
4. What is the most used WHERE condition for SELECTs?

I know it depends on the application, but there must be some statistics. Like the number of car accidents every country reports, it will be different for every country, but the statistics exist. For databases I can't find anything.