Oracle error - ORA-01109 database not open

This morning, when I was trying to troubleshoot the Oracle database using sqlplus console I got this error:

ORA-01109 database not open

So I need to open the database:

C:\> sqlplus /@PSPRODDB as sysdba
SQL> select status from v$instance;

the result should be MOUNTED. If not, try:

SQL> startup  mount;


SQL> alter database open;