vbemos posted some nice started examples for manipulating hte DB. Always learn the commands, it makes life so much easier as you learn and try to do more with them.
I also suggest you check out some of the tools posted in
http://www.everquestserver.com/forum...ic.php?t=11105
Both for file editing/comparing, and the MYsql GUI apps that make viewing data SOOOOO much nicer. Note you still have to know the commands vbemos posted!
As far as merging Databases... that is really a tough on to do bucause there are so many issues involved. At the very least I imaging it would take wrighting an external application that would take all the data that is referanced by ID elsewhere in the DB, and combine it. Then go back and insert that into the existing DB.
This applies to spawns, loot, factions, vendors.... vendors are fairly easy, Get all the items for a given vendor, plus the vendor name, and zone. Then after you had merged the spawns you would have to look up the ID of the spawn that originally had it (based on name and zone) and apply the items to that vendor. But you also have to make sure you didn't duplicate items on a vendor... so you se even for a "simple" example there is a lot to do.