Oracle 12c New Features for Developers

Oracle Database 12c introduces a new multitenant architecture that makes it easy to deploy and manage database clouds. Oracle 12c is a pluggable database environment, where we can plug multiple databases into single database container. All these databases then share same background processes and memory. This helps in reducing the overhead of managing multiple databases.

I have tried to compile some of the important new features of Oracle Database 12c. Below are the top 15 new features of Oracle Database 12c for Oracle Developer & professional.

1. Sequence as Default Value
With Oracle Database 12c, we can directly assign sequence nextval as a default value for a column, So you no longer need to create a trigger to populate the column with the next value of sequence, you just need to declare it with table definition.

Example:

create sequence test_seq start with 1 increment by 1 nocycle;

create table test_tab
(
    id number default test_seq.nextval primary key
);

2. Invisible column:
Oracle Database 12c provides you the Invisible column feature. A Column defined as invisible, will not appear in generic queries (select * from). An Invisible Column need to be explicitly referred to in the SQL statement or condition. Also invisible column must be explicitly referred in INSERT statement to insert the database into invisible columns.

Example:

SQL> create table my_table
  2  (
  3  id number,
  4  name varchar2(100),
  5  email varchar2(100),
  6  password varchar2(100) INVISIBLE
  7  );
  
SQL> ALTER TABLE my_table MODIFY (password visible);  

3. Multiple indexes on the same column
Before Oracle Database 12c, we could not have multiple indexes on a single column. In Oracle Database 12c a column may have multiple indexes but all should be of different types. Like a column may have B-Tree and BitMap Index both. But, only one index will be used at a given time.


4. VARCHAR2 length up to 32767
Form Oracle Database 12c, a varchar2 column can be sized upto 32767, which was earlier 4000. The maximum size of the VARCHAR2, NVARCHAR2, and RAW data types has been increased from 4,000 to 32,767 bytes. Increasing the allotted size for these data types allows users to store more information in character data types before switching to large objects (LOBs).


5. Top-N feature
A Top-N query is used to retrieve the top or bottom N rows from an ordered set. Combining two Top-N queries gives you the ability to page through an ordered set
Example:

SQL> SELECT value
  2  FROM   mytable
  3  ORDER BY value DESC
  4  FETCH FIRST 10 ROWS ONLY;

6. IDENTITY Columns
In Oracle Database 12c, We can define Table columns with SQL keyword IDENTITY which is a American National Standards Institute (ANSI) SQL keyword. Which are auto-incremented at the time of insertion (like in MySQL).
Example:

SQL> create table my_table
  2  (
  3  id number generated as identity,
  4  name varchar2(100),
  5  email varchar2(100),
  6  password varchar2(100) INVISIBLE
  7  );

7. With Clause improvement
In Oracle 12c, we can declare PL/SQL functions in the WITH Clause of a select statement and use it as an ordinary function. Using this construct results in better performance as compared with schema-level functions
Example:

SQL> WITH
  2    FUNCTION f_test(n IN NUMBER) RETURN NUMBER IS
  3    BEGIN
  4      RETURN n+1;
  5    END;
  6  SELECT f_test(1)
  7  FROM   dual
  8  ;

8. Cascade for TRUNCATE and EXCHANGE partition.
With Oracle Database 12c, The TRUNCATE can be executed with CASCADE option which will also delete the child records.


9. Online RENAME/MOVE of Datafiles
Oracle Database 12c has provided a simple way to online renamed or moved data files by simply "ALTER DATABASE MOVE DATAFILE" command. Data files can also be migrated online from ASM to NON-ASM and NON-ASM to ASM easily now.

Examples:

Rename datafile:  
  SQL> ALTER DATABASE MOVE DATAFILE '/u01/oradata/indx.dbf' TO '/u01/oradata/indx_01.dbf';
Move Datafile:    
  SQL> ALTER DATABASE MOVE DATAFILE '/u01/oradata/indx.dbf' TO '/u01/oradata/orcl/indx.dbf';
NON-ASM to ASM:   
  SQL> ALTER DATABASE MOVE DATAFILE '/u01/oradata/indx.dbf' TO '+DISKGROUP_DATA01';

10. Move table partition to different Tablespace online
From Oracle 12c, it become very easy to move Table Partition to different tablespace and does not require complex steps
Example:

  SQL> ALTER TABLE MY_LARGE_TABLE MOVE PARTITION MY_LARGE_TABLE_PART1 TO TABLESPACE USERS_NEW;

11. Temporary Undo
Before Oracle Database 12c, undo records of temporary tables used to be stored in undo tablespace. With the temporary undo feature in Oracle Database 12c, the undo records of temporary tables can now be stored in a temporary table instead of stored in undo tablespace. The main benefits of temporary undo are 1) Low undo tablespace usages 2) less redo data generation. For using this feature Compatibility parameter must be set to 12.0.0 or higher and TEMP_UNDO_ENABLED initialization parameter must be Enabled.


12. DDL logging
By using the ENABLE_DDL_LOGGING initiation parameter in Oracle Database 12c, we can now log the DDL action into xml and log files to capture when the drop or create command was executed and by whom under the $ORACLE_BASE/diag/rdbms/DBNAME/log|ddl location. The parameter can be set at the database or session levels.
Example:

  SQL> ALTER SYSTEM SET ENABLE_DDL_LOGGING=TRUE;

13. PGA_AGGREGATE_LIMIT parameter
Oracle Database 12c has provided us a way to limit PGA by PGA_AGGREGATE_LIMIT parameter. Before Oracle Database 12c there was no option to limit and control the PGA size. Oracle will automatically abort the session that holds the most untenable PGA memory when PGA limits exceeds the defined value.


14. SQL statement in RMAN
From Oracle Database 12c, we can execute any SQL and PL/SQL commands in RMAN without SQL prefix
Example:

  RMAN> SELECT username,machine FROM v$session;

15. Turning off redo for Data Pump the import
The new TRANSFORM option, DISABLE_ARCHIVE_LOGGING, to the impdp command line causes Oracle Data Pump to disable redo logging when loading data into tables and when creating indexes. This feature provides a great relief when importing large tables, and reduces the excessive redo generation, which results in quicker imports. This attribute applies to tables and indexes.
Example:

  impdp directory=mydir dumpfile=mydmp.dmp logfile=mydmp.log TRANSFORM=DISABLE_ARCHIVE_LOGGING:Y