ORA-30751: cannot disable column string from storing objects of type string.string
Cause: The user is trying to drop a type from being stored in a substitutable column or table. This error is raised due to one of the following reasons :
– the column is enabled to store instances of some subtype of the type being dropped.
– the column is enabled to store instances of only one type
Action: Fix the cause of the error and retry the operation.
ORA-30751错误是oracle中一种使用Allowing不正确时出现的常见错误。
错误说明：
ORA-30751是由于你正在尝试将对象类型（如字符串）存储在不允许这样做的列中，而导致的一种错误。
ORA-30751错误通常发生在当你尝试使用以下语句来创建对象类型的表时：
CREATE TABLEtablename
(
columnname VARCHAR2(50) ALLOWING OBJECTS OF TYPE string
)
当你尝试执行上述操作时，ORA-30751错误将被触发。
解决方法：
解决ORA-30751错误的最佳方法是将ALLOWING选项从你想要存储对象类型的列中删除，以便ORACLE可以正确理解。例如，以下语句将消除错误：
CREATE TABLEtablename
(
columnname VARCHAR2(50)
)
然后，您可以安全地为该列存储对象类型，而不会出现ORA-30751错误。