文档解释
ORA-30512: cannot modify string.string more than once in a transaction
Cause: An attempt was made to modify an object more than once in a transaction. This error is usually caused by a DDL statement that fires a system trigger that tries to modify the same object. It can also happen when an attempt is made to perform more than one DDL operation on a queue table in the same transaction without issuing a commit between operations.
Action: Do not create system triggers that might modify an already modified object. Also, do not specify more than one DDL operation on a queue table in the same transaction.
ORA-30512错误指示用户不能在一个事务中多次修改字符串变量。
官方解释
ORA-30512 occurs when an attempt is made to modify a string type more than once within one transaction. It is similar to the error ORA-06512 which occurs when an attempt is made to modify a numeric type more than once within one transaction.
常见案例
这个错误通常出现在内部存储过程使用影响到字符串变量的语句（例如UPDATE）的情况下，程序在同一事务中对字符串变量进行了多次操作。
一般处理方法及步骤
1.检查程序中的事务判断，或者单步调试程序，确认字符串变量被操作的次数。
2.如果字符串变量被多次操作，需要将程序中的事务判断修改，使得每次修改字符串变量为一个事务，以避免程序中出现ORA-30512错误。
3.检查系统是否正常工作，若仍然出现状态30512，请重启数据库，以确保数据库正常工作。
