フリー問題

問題文

A block assigns a sequence value to a local variable, and a later statement in the same block names that same sequence again. The block then rolls back. Which description of what happens to the sequence is correct?

選択肢

1. The engine keeps the pseudocolumn cached for the transaction, so the second reference returns the prior number, and the advance is applied when the transaction commits.
2. The engine evaluates the pseudocolumn once for the whole block, so the second reference returns the same number, and the rollback puts the sequence back to where it stood before.
3. The engine evaluates every occurrence of the pseudocolumn, so the second reference advances the sequence again, and the advance stands even after the block has been rolled back.
4. The engine rejects the pseudocolumn inside a PL/SQL expression, so the value must be read with a query on a table, and the advance happens when the block reaches its end.