Final answer:
The ORA-02270 error occurs when trying to reference a column that is not a unique or primary key in another table, and it can be fixed by ensuring the foreign key matches the referenced primary or unique key.
Step-by-step explanation:
The error ORA-02270 is a database error code from Oracle that indicates a problem with a foreign key constraint. When you encounter this error, it means that you are trying to create a foreign key that references a column which is not a unique or primary key in the referenced table. In relational database design, a foreign key must correspond to a unique identifier in another table, typically a primary key, to maintain referential integrity.
To fix the ORA-02270 error, you need to ensure that the foreign key in your columnlist exactly matches the unique or primary key in the referenced table. This includes making sure that the columns in the foreign key have the same data type and order as the columns in the referenced unique or primary key.
For example, if you're trying to reference the primary key of a 'users' table from a 'orders' table, the foreign key in 'orders' should refer to the primary key column of 'users', and both should have the same data types configured.