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，要盡量使用普通用戶，因為很多事務級別的設置，對于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(shù)據(jù)字典以方便實驗的目的可給用戶賦予如下權限：
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)
分享題目：OracleSYS用戶無法設置session級別的readonly
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