Oracle SYS用戶無法設置session級別的read only

官方文檔參考：
SYSDBA is used internally in the Oracle database and has specialized functions. Its behavior is not the same as for generalized users. For example, the SYS user cannot do a transaction level consistent read (read-only transaction). Queries by SYS will return changes made during the transaction even if SYS has set the transaction to be READ ONLY.  Therefore export parameters like CONSISTENT, OBJECT_CONSISTENT, FLASHBACK_SCN, and FLASHBACK_TIME cannot be used.

進行Oracle事務相關的實驗時，要儘量使用普通用戶，因為很多事務級別的設置，對於sqlplus / as sysdba連入方式無法獲得正確的結果。
如果想給用戶獲取數據字典以方便實驗的目的可給用戶賦予如下許可權：
GRANT CONNECT,RESOURCE,SELECT ANY DICTIONARY,SELECT ANY TABLE TO TUSER;



參考：How To Connect As SYSDBA When Using Export Or Import (文檔 ID 277237.1)