Some 12C Features

Will try to describe some of the 12C features and will keep editing this post.

Note:

• If you want to install Oracle 12 on Windows 7, refer the steps here 
• To troubleshoot invalid common user or role name after installation, go here

Feature List

 Identity Columns:

• Also known as auto-number column. This implies that the data in the column should increase when data is inserted).
• Read article on the same here.

 Invisible Columns:

• Columns can be made invisible
• It gives one the ability to introduce a change while minimizing any negative side effects of that change.
• Read article on the same here 

With Clause:

• Instead of using a stored PL/SQL function, we can include the body of the function in the SQL query
• Read article on the same here 

 Truncate statements with the cascade option

• We could not truncate table with foreign key constraints.
• Now in 12c, one can execute the truncate table command with the cascade option (to cascade through the child tables).
• Note: You would need to create the foreign key with the "on delete cascade" option

Columns can have a default value in place of NULL

• You can define a column to have a default value when NULL is inserted
• e.g. create table ......  product_id NUMBER ON NULL 0,.....
• So if one explicity inserts NULL, it will be populated by value 0

Multiple Index - same columns

• You can create multiple indexes (different types) on a same set of columns.
• Assume you need to change from B*tree to Bitmap or vice versa.
• You need not drop the index.
• Just make the first index invisible and make a new index.
• Conditions:
• Different types of indexes
• Different uniqueness
• Different partitions are used

 

12 C Feature - Invisible Columns

Note: Index article on some 12c features can be seen here

The name is self explanatory.
Invisible columns means just that -- columns that are invisible.
It gives one the ability to introduce a change while minimizing any negative side effects of that change.

So, in a table, if we add a column, it will show up in a "select *" query.
All the "insert into <table> values ...." queries will break.

When you add an invisible column, you won't be able to see it even when you execute a "DESC" or when you run a "select *" query.
The "insert into <table> values ...." queries will not break.
However, you will able to see it if you specifically query for it by name.

Lets have a look at an example.
We have a table "TEST_IDENTITY" which we had used to test the identity column. Refer article on identity column

Lets add an invisible column to it.
The command will be:

ALTER TABLE <TABLE_NAME> ADD (<COLUMN_NAME> <TYPE> INVISIBLE);

As you can see below, I added a column name as INVISIBLE and it does not show up in DESC command.
It does not show up in "select *" and has no impact on the "insert into <TABLE_NAME>" as well.

But you can insert data into it and also do a select by calling it explicitly.

You can make the column visible by running the following alter command:
ALTER TABLE <TABLE_NAME> MODIFY <INVISIBLE_COLUMN_NAME> VISIBLE;

Some questions that may help:

How to know a table exists with an invisible column?

Run a query on USER_TAB_COLS
SELECT COLUMN_NAME, HIDDEN_COLUMN FROM USER_TAB_COLS WHERE TABLE_NAME = '<TABLE_NAME>';

What if I create an invisible column as NOT NULL?
INSERT will fail. You need to create with DEFAULT option or use a trigger to populate on INSERT.

Is there any massive advantage of this feature?
Its a feature which could be used but not any with massive advantage. it could create problems for some applications when made visible, but if you have coded with proper INSERTs/SELECTs (mentioning columns), it won't harm your application.