Old Databases in new zen cart problems?

If I was to use an old version of a database on the new version of zen cart what would happen?

Is there anyway of knowing what version the old database is?

You can see version info in ZC's admin console:-

Admin...Tools...Server/Version info

There are usually database alterations with each version upgrade. In short, using an older database with a newer version is inadvisable, and in all likelihood, will not work.

... better to UPGRADE, using the proper procedure.

Note: Upgrading properly will preserve the information you have in your old database.

Does this mean you must re-enter every stock item again?
I am upgrading from ZenCart 1.2.7.

Surely this isn't the case as it would be ridiculously time consuming !

If thats the case I wouldn't want to upgrade.

You'll notice if you follow the upgrade documentation that comes in each release that instructions for upgrading your existing database content are included as part of the steps you need to follow.

Thanks ! I will give it a go !