Usage of 'which'

[smohit04]

"John has a good understanding of business and technology, which most people don't have."

Is the usage of 'which' correct in this sentence?

My confusion is that generally which is used to modify the noun preceding immediately before ',' but in this case it should be modifying 'good understanding' because business and technology are in a propositional phrase modifying 'good understanding' and as per our strategy guide - the noun in a prepositional phrase cannot be the subject of the sentence.

Please confirm if I understand it correctly. The sentence is created by me only and not taken from any source.

[tim]

please see
post31162.html#p31162
for Ron's explanation of the usage of "which"..