Oracle database 19c pl/sql  examples

### connect database
> sqlplus / nolog
> sqlplus / as sysdba
> sqlplus  sys/pw@host/service_name AS SYSDBA 

###  show cdb pdb
- Determining Whether a Database is a CDB
> SELECT CDB FROM V$DATABASE;
> show con_name;
> show pdbs;

- alter pdb open or close
> ALTER PLUGGABLE DATABASE pdb1 OPEN
> ALTER PLUGGABLE DATABASE pdb1 CLOSE

