task#1 Check the version of your Oracle database and if it is not 12c, notify that it should be upgraded to the Oracle Database 12c.

step#1 – Connect to the Oracle Database as SYSDBA

c:TEMP>sqlplus / as sysdba
SYS@orcl > spool task#1.ext append

step#2 – Check the database version

SYS@orcl > select value from v$parameter where name='optimizer_features_enable';
VALUE
-----------------------------------------------------------
12.1.0.2
SYS@orcl > select value from v$parameter where name='db_unique_name';
VALUE
---------
orcl

The other way to know the Oracle Database version is the following:

--Oracle Database 10.2 
SQL> begin 
2 dbms_output.put_line(DBMS_DB_VERSION.VERSION || '.' || DBMS_DB_VERSION.RELEASE); 
3 end; 
4 / 
10.2

--Oracle Database 12.1
SYS@orcl > begin
  2  dbms_output.put_line(DBMS_DB_VERSION.VERSION || '.' || DBMS_DB_VERSION.RELEASE);
  3  end;
  4  /
12.1

step#3 – If the database is not Oracle Database 12c, show the following message ” current_version should be updated to Oracle database 12c. Go to the www.oracle.com ” , and go to step#8.

SYS@orcl > select value current_version,
case substr(value,1,2) 
  when '12' then 'The current version is ' || value
  else value || ' should be updated to Oracle Database 12c. Go to www.oracle.com'
end as status
from v$parameter
where name='optimizer_features_enable';
/
VERSION       STATUS
------------- -----------------------------------------------
12.1.0.2      The current version is 12.1.0.2

step#4 – Else, if it is Oracle Database 12c, show CDB/PDBs details

SYS@orcl > select con_id, name, open_mode, restricted from v$containers;
CON_ID     NAME         OPEN_MODE  RES
------     -----------  --------  ---
1          CDB$ROOT     READ WRITE NO
2          PDB$SEED     READ ONLY  NO
3          PDBORCL      MOUNTED    NO

step#5 – If any PDB is not opened, set its mode to READ ONLY or READ WRITE accordingly

SYS@orcl > select con_id, name
from v$containers
where open_mode not IN ('READ WRITE', 'READ ONLY');
CON_ID     NAME
---------- ------------------------------
3          PDBORCL

SYS@orcl > alter pluggable database pdborcl open read write;
Pluggable database altered.

SYS@orcl > select con_id, name, open_mode, restricted 
from v$containers 
where name='PDBORCL';
/
CON_ID     NAME                           OPEN_MODE  RES
---------- ------------------------------ ---------- ---
3          PDBORCL                        READ WRITE NO

step#6 – Connect to the last PDB that is opened in READ WRITE mode.

SYS@orcl > alter session set container=pdborcl;
Session altered.

step#7 – Show the container ID of the PDB

SYS@orcl > sho con_id
CON_ID
------------------------------
3
SYS@orcl > sho parameter plsql
NAME                   TYPE        VALUE
-------------------    ----------- ------------------------------
plsql_ccflags          string
plsql_code_type        string      INTERPRETED
plsql_debug            boolean     FALSE
plsql_optimize_level   integer     2
plsql_v2_compatibility boolean     FALSE
plsql_warnings         string      DISABLE:ALL

step#8 – Disconnect from the database.

SYS@orcl > exit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
c:TEMP>type task#1.ext | more

task#2 Automate task#1. Create a standalone procedure that will return the same result as task#1.

create or replace function funct_db_version
  return number
  authid current_user
is
  l_intval number;
  l_strval varchar2(2000);
  l_type number;
begin
  l_type := dbms_utility.get_parameter_value ('optimizer_features_enable', l_intval, l_strval);
  return to_number(substr(l_strval,1,2));
exception
  when others then
    dbms_output.put_line(SQLERRM);
end;
/

--Oracle Database 10.2
select funct_db_version from dual;

FUNCT_DB_VERSION
----------------
              10

--Oracle Database 12.1
SYS@orcl > select funct_db_version from dual;

FUNCT_DB_VERSION
----------------
              12

create or replace procedure proc_upgrade_to_12c
  authid current_user
is
  l_stmt varchar2(500);
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
  CURSOR cur_id_name
  is 
  select con_id, name from v$containers where open_mode not IN ('READ WRITE', 'READ ONLY');
  TYPE t_id is table of v$containers.con_id%TYPE;
  TYPE t_name is table of v$containers.name%TYPE;
  l_list_id t_id;
  l_list_name t_name;
  l_con_id varchar2(256);
  l_con_name varchar2(256);
$END
begin
  if not funct_db_version = 12 then
    dbms_output.put_line(' The database ' ||DBMS_DB_VERSION.VERSION || '.' || DBMS_DB_VERSION.RELEASE || ' should be updated to Oracle Database 12c. Go to www.oracle.com' );
    return;
  end if;
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
  if not cur_id_name%ISOPEN then
    open cur_id_name;
  end if; 
  fetch cur_id_name BULK COLLECT into l_list_id, l_list_name;
  if l_list_id.COUNT > 0 then
    for i in 1..l_list_id.COUNT
    loop
      l_stmt := 'alter pluggable database ' ||lower( l_list_name(i) )|| ' open read write';
      execute immediate l_stmt;
      dbms_output.put_line('Container ' || lower( l_list_name(i) )|| ' open READ WRITE');
    end loop;
  end if; 
  select sys_context('USERENV','CON_ID') into l_con_id from dual;
  select sys_context('USERENV','CON_NAME') into l_con_name from dual;
  dbms_output.put_line('Current container ' || l_con_name || ' has ID ' || l_con_id);
  dbms_output.put_line('$$PLSQL_CODE_TYPE = ' || $$PLSQL_CODE_TYPE);
  dbms_output.put_line('$$PLSQL_OPTIMIZE_LEVEL = ' || $$PLSQL_OPTIMIZE_LEVEL);
  dbms_output.put_line('$$PLSCOPE_SETTINGS = ' || $$PLSCOPE_SETTINGS);
  if cur_id_name%ISOPEN then
    close cur_id_name;
  end if;
$END
exception
  when others then
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
  if cur_id_name%ISOPEN then
    close cur_id_name;
  end if;
$END
  dbms_output.put_line(SQLERRM);
end proc_upgrade_to_12c;
/

--Oracle Database 10.2
SQL>exec proc_upgrade_to_12c;

The database 10.2 should be updated to Oracle Database 12c. Go to www.oracle.com

PL/SQL procedure successfully completed.

--Oracle Database 12.1
SYS@orcl > exec proc_upgrade_to_12c;
Current container CDB$ROOT has ID 1
$$PLSQL_CODE_TYPE = INTERPRETED
$$PLSQL_OPTIMIZE_LEVEL = 2
$$PLSCOPE_SETTINGS = IDENTIFIERS:NONE

PL/SQL procedure successfully completed.

task#3 Create a standalone procedure that shows details of CDB/PDBs such as container id, name, and open mode.

create or replace procedure proc_show_details_12c
  authid current_user
  is
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
  CURSOR cur_id_name_mode 
  is 
  select con_id, name, open_mode from v$containers;
  TYPE t_id is table of v$containers.con_id%TYPE;
  TYPE t_name is table of v$containers.name%TYPE;
  TYPE t_mode is table of v$containers.open_mode%TYPE;
  l_list_id t_id;
  l_list_name t_name;
  l_list_mode t_mode;
  l_con_id varchar2(256);
  l_con_name varchar2(256);
  l_stmt varchar2(500);
$END
begin
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
  if funct_db_version = 12 then
    if not cur_id_name_mode%ISOPEN then
      open cur_id_name_mode;
    end if; 
    fetch cur_id_name_mode BULK COLLECT into l_list_id, l_list_name, l_list_mode;
    if l_list_id.COUNT > 0 then
      for i in 1..l_list_id.COUNT
      loop
        if l_list_name(i) = 'CDB$ROOT' then
          dbms_output.put_line('Root ' || l_list_id(i) || ', ' || l_list_name(i) || ' open as ' || l_list_mode(i) );
        else
          dbms_output.put_line('Pluggable DB ' || l_list_id(i) || ', ' || l_list_name(i) || ' open as ' || l_list_mode(i) );
        end if;
      end loop; 
    end if;
    if cur_id_name_mode%ISOPEN then
      close cur_id_name_mode;
    end if; 
  end if;
$ELSE
  dbms_output.put_line('Version '|| DBMS_DB_VERSION.VERSION || '.' || DBMS_DB_VERSION.RELEASE || 
  ' does not support this code. Upgrade to 12c.');
$END
exception
  when others then
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
  if cur_id_name_mode%ISOPEN then
    close cur_id_name_mode;
  end if;
$END
  dbms_output.put_line(SQLERRM);
end proc_show_details_12c;
/

--Oracle Database 10.2
SQL> exec proc_show_details_12c;
Version 10.2 does not support this code. Upgrade to 12c.

PL/SQL procedure successfully completed.

--Oracle Database 12.1
SYS@orcl > exec proc_show_details_12c;
Root 1, CDB$ROOT open as READ WRITE
Pluggable DB 2, PDB$SEED open as READ ONLY
Pluggable DB 3, PDBORCL open as READ WRITE

PL/SQL procedure successfully completed.

Or, you can see all the above actions in a SQL*Plus Command Line Window:

Alter The Mode Of The Pluggable Database

task#4 Create a package with procedures that will return the same result as task#2 and task#3.

create or replace package pkg_checker
is
  function funct_db_version return number;
  procedure proc_show_details_12c;
  procedure proc_upgrade_to_12c;
end;
/

create or replace package body pkg_checker
is
  function funct_db_version
  return number
  is
    l_intval number;
    l_strval varchar2(2000);
    l_type number;
  begin
    l_type := dbms_utility.get_parameter_value ('optimizer_features_enable', l_intval, l_strval);
    return to_number(substr(l_strval,1,2));
  exception
    when others then
      dbms_output.put_line(SQLERRM);
  end;

  procedure proc_show_details_12c
  is
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
    CURSOR cur_id_name_mode
    is 
    select con_id, name, open_mode from v$containers;
    TYPE t_id is table of v$containers.con_id%TYPE;
    TYPE t_name is table of v$containers.name%TYPE;
    TYPE t_mode is table of v$containers.open_mode%TYPE;
    l_list_id t_id;
    l_list_name t_name;
    l_list_mode t_mode;
    l_con_id varchar2(256);
    l_con_name varchar2(256);
    l_stmt varchar2(500);
$END
  begin
    if not funct_db_version = 12 then
      dbms_output.put_line( 'The database ' || DBMS_DB_VERSION.VERSION || '.' || DBMS_DB_VERSION.RELEASE || ' should be updated to Oracle Database 12c. Go to www.oracle.com' );
      return;
    end if;
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
    if not cur_id_name_mode%ISOPEN then
      open cur_id_name_mode;
    end if; 
    fetch cur_id_name_mode BULK COLLECT into l_list_id, l_list_name, l_list_mode;
    if l_list_id.COUNT > 0 then
      for i in 1..l_list_id.COUNT
      loop
        if l_list_name(i) = 'CDB$ROOT' then
          dbms_output.put_line('Root ' || l_list_id(i) || ', ' || l_list_name(i) || ' open as ' || l_list_mode(i) );
        else
          dbms_output.put_line('Pluggable DB ' || l_list_id(i) || ', ' || l_list_name(i) || ' open as ' || l_list_mode(i) );
        end if;
      end loop; 
    end if;
    if cur_id_name_mode%ISOPEN then
      close cur_id_name_mode;
    end if; 
$END
  exception
    when others then
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
    if cur_id_name_mode%ISOPEN then
      close cur_id_name_mode;
    end if;
$END
    dbms_output.put_line(SQLERRM);
  end;

  procedure proc_upgrade_to_12c
  is
    l_stmt varchar2(500);
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
    CURSOR cur_id_name
    is 
    select con_id, name from v$containers where open_mode not IN ('READ WRITE', 'READ ONLY');
    TYPE t_id is table of v$containers.con_id%TYPE;
    TYPE t_name is table of v$containers.name%TYPE;
    l_list_id t_id;
    l_list_name t_name;
    l_con_id varchar2(256);
    l_con_name varchar2(256);
$END
  begin
    if not funct_db_version = 12 then
      dbms_output.put_line('The database ' || DBMS_DB_VERSION.VERSION || '.' || DBMS_DB_VERSION.RELEASE || ' should be updated to Oracle Database 12c. Go to www.oracle.com' );
      return;
    end if;
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
    if not cur_id_name%ISOPEN then
      open cur_id_name;
    end if; 
    fetch cur_id_name BULK COLLECT into l_list_id, l_list_name;
    if l_list_id.COUNT > 0 then
      for i in 1..l_list_id.COUNT
      loop
        l_stmt := 'alter pluggable database ' ||lower( l_list_name(i) )|| ' open read write';
        execute immediate l_stmt;
        dbms_output.put_line('Container ' || lower( l_list_name(i) )|| ' open READ WRITE' ) ;
      end loop;
    end if;
    select sys_context('USERENV','CON_ID') into l_con_id from dual;
    select sys_context('USERENV','CON_NAME') into l_con_name from dual;
    dbms_output.put_line('Container ' || l_con_name || ' has ID ' || l_con_id);
    dbms_output.put_line('$$PLSQL_CODE_TYPE = ' || $$PLSQL_CODE_TYPE);
    dbms_output.put_line('$$PLSQL_OPTIMIZE_LEVEL = ' || $$PLSQL_OPTIMIZE_LEVEL);
    dbms_output.put_line('$$PLSCOPE_SETTINGS = ' || $$PLSCOPE_SETTINGS);
    if cur_id_name%ISOPEN then
      close cur_id_name;
    end if;
$END
  exception
    when others then
$IF DBMS_DB_VERSION.VERSION >= 12 $THEN
    if cur_id_name%ISOPEN then
      close cur_id_name;
    end if;
$END
    dbms_output.put_line(SQLERRM);
  end;
end;
/

--Oracle Database 10.2
SQL> exec pkg_checker.proc_show_details_12c;
The database 10.2 should be updated to Oracle Database 12c. Go to www.oracle.com

PL/SQL procedure successfully completed.

--Oracle Database 12.1
SYS@orcl > exec pkg_checker.proc_show_details_12c;
Root 1, CDB$ROOT open as READ WRITE
Pluggable DB 2, PDB$SEED open as READ ONLY
Pluggable DB 3, PDBORCL open as READ WRITE

PL/SQL procedure successfully completed.

--Oracle Database 10.2
SQL> exec pkg_checker.proc_upgrade_to_12c;
The database 10.2 should be updated to Oracle Database 12c. Go to www.oracle.com

PL/SQL procedure successfully completed.

--Oracle Database 12.1
SYS@orcl > exec pkg_checker.proc_upgrade_to_12c;
Container CDB$ROOT has ID 1
$$PLSQL_CODE_TYPE = INTERPRETED
$$PLSQL_OPTIMIZE_LEVEL = 2
$$PLSCOPE_SETTINGS = IDENTIFIERS:NONE

PL/SQL procedure successfully completed.

Now, you can repeat the process over and over again, see the SQL*Plus Command Line Window:

Repeat the Action Over and Over Again

So far, the following schema objects were created:

--Oracle Database 10.2
SYS$SQL> 
select substr(object_name,1,20), substr(object_type,1,20)
from user_objects  
where created > sysdate - 1;

SUBSTR(OBJECT_NAME,1 SUBSTR(OBJECT_TYPE,
-------------------- -------------------
PROC_UPGRADE_TO_12C  PROCEDURE
PROC_SHOW_DETAILS_12 PROCEDURE
PKG_CHECKER          PACKAGE
PKG_CHECKER          PACKAGE BODY
FUNCT_DB_VERSION     FUNCTION

--Oracle Database 12.1
SYS@orcl > select lpad(substr(object_type,1,20),20) type, substr(object_name,1,20) name, created --12.1
  2  from user_objects
  3  where object_name like 'FUNCT%'
  4  or object_name like 'PROC%'
  5  or object_name like 'PKG%';

TYPE                 NAME                 CREATED
-------------------- -------------------- ---------
             PACKAGE PKG_CHECKER          21-AUG-15
        PACKAGE BODY PKG_CHECKER          21-AUG-15
           PROCEDURE PROC_SHOW_DETAILS_12 21-AUG-15
           PROCEDURE PROC_UPGRADE_TO_12C  21-AUG-15
            FUNCTION FUNCT_DB_VERSION     21-AUG-15

10 rows selected.

Final Task# Drop all objects from the database that were created in the above examples!

SYS@orcl > drop function funct_db_version;
SYS@orcl > drop procedure proc_upgrade_to_12c;
SYS@orcl > drop procedure proc_show_details_12c;
SYS@orcl > drop package pkg_checker;

Instead of Summary

The purpose of the task#1 is to show how many solutions you can create for the one task, in this case it was to find out the version and the release of the Oracle Database. This can also be done easily with this select statement:

c:TEMP>sqlplus / as sysdba

SQL*Plus: Release 12.1.0.2.0 Production on Thu Sep 10 18:14:23 2015

Copyright (c) 1982, 2014, Oracle.  All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

SYS@orcl > COL PRODUCT FORMAT A40
SYS@orcl > COL VERSION FORMAT A15
SYS@orcl > COL STATUS FORMAT A15
SYS@orcl > SELECT * FROM PRODUCT_COMPONENT_VERSION;

PRODUCT                               VERSION    STATUS
------------------------------------ ----------  ------------
NLSRTL                               12.1.0.2.0  Production
OracleDatabase12c Enterprise Edition 12.1.0.2.0  64bit Production
PL/SQL                               12.1.0.2.0  Production
TNS for 64-bit Windows:              12.1.0.2.0  Production

SYS@orcl >

Dictionary
sqlplus = “SQL*Plus is an interactive and batch query tool that is installed with every Oracle Database installation. It has a command-line user interface.”, [ref2]
spool = SQL*Plus command that stores query results in a file, or optionally sends the file to a printer, [ref2]
.ext = the extension of the file where command spool stores the query results, [ref2]
append = The option that adds the contents of the buffer to the end of the file you specify in the spool command, [ref2]
CDB = a multitenant container database,
PDB = a pluggable database,
v$parameter = The dynamic performance view that displays information about the initialization parameters that are currently in effect for the session, [ref3]
v$containers = The dynamic performance view that displays information about PDBs and the root associated with the current instance, [ref3]
select = SQL statement that retrieves data from one or more tables, object tables, views, object views, or materialized views, [ref1]
CDB$ROOT = Oracle Database 12c root container, [ref4]
PDB$SEED = Oracle Database 12c seed PDB, [ref4]
PDBORCL = Oracle Database 12c pluggable database, a user-created entity that contains the data and code required for a specific set of features, [ref4]
READ ONLY = A database that is available for queries only and cannot be modified, [ref4]
READ WRITE = A database that is available for queries and that can be modified, [ref4]
MOUNTED = An database instance that is started and has the database control file open, [ref4]
alter pluggable database = SQL statement that modifies a pluggable database (PDB), [ref1]
alter session = SQL statement that sets or modifies any of the conditions or parameters that affect your connection to the database. The statement stays in effect until you disconnect from the database, [ref1]
show user = SQL*Plus command that shows the username you are currently using to access SQL*Plus, [ref2]
show con_id = SQL*Plus command that displays the id of the Container to which you are connected when connected to a Consolidated Database. If issued when connected to a non-Consolidated Database, this command returns 0, [ref2]
exit = SQL*Plus command that let you exit SQL*Plus, [ref2]
case = SQL expressions that let you use IF … THEN … ELSE logic in SQL statements without having to invoke procedures, [ref1]

Further reading
If you want to be familiar with Oracle SQL, please see [ref1].
If you want to know what kind of the CLI (Command Line Interface) SQL*Plus is, please see [ref2].
if you want to know details of the Oracle Database meta data, please see [ref3].
If you want to understand the Oracle Database architecture, please see [ref4].
If you want to know details of PL/SQL (Oracle extension of SQL), please see [ref5].

References
[ref1] SQL*Plus® User’s Guide and Reference Release 12.1 E18404-12
[ref2] Oracle® Database SQL Language Reference 12c Release 1 (12.1) E41329-09
[ref3] Oracle® Database Reference 12c Release 1 (12.1) E41527-15
[ref4] Oracle® Database Concepts 12c Release 1 (12.1) E41396-12
[ref5] Oracle® Database PL/SQL Language Reference 12c Release 1 (12.1) E50727-04
[ref6] Oracle® Database PL/SQL Packages and Types Reference 12c Release 1 (12.1)
E41829-05