Oracle Database related Questions

Here there are very basic still sometime become critical to know concept if you working in Oracle Database related activities. 

 

 

 

Q: What is a view?

A view is a tailored presentation of the data contained in one or more tables(or other views). Unlike a table, a view is not allocated any storage space, nor does a view actually contain data; rather, a view is defined by a query that extracts or derives data from the tables the view references. These tables are called base tables. Views present a different representation of the data that resides within thebase tables. Views are very powerful because they allow you to tailor the presentation of data to different types of users. Views are often used to:

• provide an additional level of table security by restricting access to a predetermined set of rows and/or columns of a table

• hide data complexity

• simplify commands for the user

• present the data in a different perspective from that of the base table

• isolate applications from changes in definitions of base tables

• express a query that cannot be expressed without using a view

 

Rules governing the relationships between primary keys and foreign keys of tables within a relational database that determine data consistency. Referential integrity requires that the value of every foreign key in every table be matched by the value of a primary key in another table.

Q: What is a cursor?A cursor is a private sql work area used to perform manipulations on data using pl\sql, mainly used for multiple row manipulations and locking columns. Data which is populated into the cursor is known as active dataset.

 

Cursors are of two types 1.implicit   2.explicit

Implicit———attributes or properties for implicit cursor

1.sql%is open:attribute returns a boolean value stating wether the cursor is open or closed.

2.sql % found: returns boolean value stating whether the record is found in the cursor.

3.sql%notfound : returns a boolean value stating whether the record is not found in the cursor

4.sql %rowcount :returns a pneumeric value stating no.of rows executed in the cursor.

Explicit cursors—retrives multiple rows, users can perform locks on th data in the cursor attributes-

1.% is open

2.% found

3.% not found

4.% rowcount

WE CAN WRITE TWO CURSORS IN ONE PROGRAM

WE CAN WRITE A CURSOR SPECIFYING PARAMETERS

CURSOR WITH UPDATE CLAUSE IS USED TO PERFORM LOCKS ON DATA.