22-10-2012, 04:10 PM
Structure Query Language
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Objective
After completing this lesson ,you should able to do the following:
Discuss the theoretical and physical aspects of a relational database.
Describe the Oracle implementation of the RDBMS.
Storing Information
Every organization has some information need. A company need to save information about employee,dept and salaries.These pieces of row fact are called data.
Organization can store data on various media and in different formats.
E.g. a hard copy document,
Or in electronics spredsheet
Or in database.
A database is a organized collection of data.
To manage database we need database management system.
A DBMS is a collection of program that stores retrieves , and modify data in database on request.
There are four main type of database:
Hierarchical,
Network,
Relational,
Object relational.
SQL is a Standard - BUT..
SQL is an ANSI (American National Standards Institute) standard computer language for accessing and manipulating database systems. SQL statements are used to retrieve and update data in a database. SQL works with database programs like MS Access, DB2, Informix, MS SQL Server, Oracle, Sybase, etc.
Data Manipulation Language (DML)
SQL (Structured Query Language) is a syntax for executing queries. But the SQL language also includes a syntax to update, insert, and delete records.
These query and update commands together form the Data Manipulation Language (DML) part of SQL:
UPDATE - updates data in a database table
DELETE - deletes data from a database table
INSERT INTO - inserts new data into a database table
Defining a Null value
If a row lacks of data values for a particular column, that value is said to be null, or to contain a null.
A null is a value that is unavailable, unassigned, unknown, inapplicable.
A null is not same as zero or blank space.