事务失败，因为在快照隔离事务内不允许此 DDL 语句。由于未对元数据进行版本控制，如果与快照隔离混合，元数据更改可能导致不一致。

Transaction failed because this DDL statement is not allowed inside a snapshot isolation transaction. Since metadata is not versioned, a metadata change can lead to inconsistency if mixed within snapshot isolation.