- Friend classes are useful when a class wants to hide features from users which are needed only by another, tightly coupled class. 

- Implementation details can be kept safe by providing friend status to a tightly cohesive class.

Insert image into a table

Create the following table:

      create table pics_table (

      bfile_id number,

      bfile_desc varchar2(30),

      bfile_loc bfile,

      bfile_type varchar2(4))

      TABLESPACE appl_data

      storage (initial 1m next 1m pctincrease 0) 

Insert Query:

      INSERT INTO pics_table

      VALUES(4,'test image',bfilename('GIF_FILES','Test.JPG'),'JPEG'); 

WATER MARK is a divided segment of used and free blocks. Blocks which are below high WATER MARK i.e. used blocks, have at least once contained some data. This data might have been deleted later. Oracle knows that blocks beyond high WATER MARK don’t have data; it only reads blocks up to the high WATER MARK during a full table scan. 

Shared pool in oracle contains cache information that collects, parses, interprets and executes SQL statements that goes against database. This shared pool acts like a buffer for these SQL statements.

Oracle supports 3 transaction isolation levels: 

- Read committed (default)

- Serializable transactions

- Read only

SQL> ALTER USER user_name ACCOUNT LOCK;

SQL> ALTER USER user_name ACCOUNT UNLOCK;

Locking is a mechanism to ensure data integrity while allowing maximum concurrent access to data. It is used to implement concurrency control when multiple users access table to manipulate its data at the same time.

Advantages :

- Avoids deadlock conditions

- Avoids clashes in capturing the resources

A Peoplesoft database is expression which point out a database containing Peoplesoft objects. For Oracle and only for Oracle, Peoplesoft consists in 3 schemas namely:

- PS (PSDBOWNER table owner),

- PEOPLE (for connection checking) and

- SYSADM (by default), the last one contains all the objects/data.

One of the database objects is connected with single Oracle schema, and all processes that connect to the database use the standard PSFT login procedure. PSFT login is used because to refer to the collection of tables in the administrative schema within an Oracle database. Every process that makes a 2-tier connection to the database identifies itself with a PSFT user or operator ID. Hence the interaction goes.