Which three statements are true about sequences in a single instance Oracle database?
A.A sequence number that was allocated can be rolled back if a transaction fails B.A sequence can only be dropped by a DBA C.Sequences can always have gaps D.A sequence can issue duplicate values. E.A sequence's unallocated cached values are lost if the instance shuts down F.Two or more tables cannot have keys generated from the same sequence正确答案CDE
