Oracle® Database 11g / 12c / 18c error codes ORA-01531: a database already open by the instance

ORA-01531: a database already open by the instance

Oracle Error Code: ORA-01531

Cause: During ALTER DATABASE, an attempt was made to open a database on an instance for which there is already an open database.

Action: If you wish to open a new database on the instance, first shutdown the instance and then startup the instance and retry the operation.