ORA-21000

The ORA-21000 error is a PL/SQL exception that occurs when trying to insert or update a record in a table with a unique constraint and the new value violates the constraint. This error is also known as "unique constraint violated".

For example, if you have a table with a unique constraint on the "email" column, and you try to insert a new record with an email address that already exists in the table, you will get the ORA-21000 error.

To resolve this error, you can either modify the value to make it unique or delete the existing record that has the same value. Alternatively, you can modify the unique constraint to allow for duplicate values, but this may not be desirable in all cases