INTRODUCTION TO SQL

Introduction

SQL is Structured Query Language. It is a language like C or COBOL but with a difference. C and COBOL are procedural languages where as SQL is non-procedural.

A procedural language allows programming constructs like if-then-else and looping logic such with ‘while’ or ‘for’ loops. To retrieve data in procedural language you must navigate, or find a path to the data record you want. Procedural languages are complex, therefore programmers not for end-users.

SQL is an English- like language. Users with little of no experience in data processing can learn SQL’s basic features very quickly. Yet it also provides programmers and data processing professionals, both for communicating application requirements and implementing solutions.

To store and retrieve data, you need commands to :

Controlling database access and other security requirements.

Create or drop table and other data structures – Data Definition Language (DDL) commands.

Query, Update, Insert or Delete from the tables – Data Manipulation Language (DML) commands.

Create user and grant privileges for security purposes – Data Control Language (DCL) commands.

SQL lets you forget about “how to do it” and focus instead on “what is to be done”. For example, with a single command you can update multiple rows in your database, without worrying about their locations, storage formats and access path.

As in other database management systems, you can use SQL statements in other Oracle tools. For example, in Oracle Forms (Oracle’s screen design and application generation tool) you can use SQL statement to manipulate data. So

Understanding SQL will let you use any other Oracle tool without learning additional syntax.

CLIENT/SERVER COMPUTING MODEL

2.7 Introductions

The problems of the LAN have led to the genesis of client/server computing model. Client/server computing (also called distributed application processing and cooperative application processing) delivers the benefits of networking computing model along with shared data access and high performance characteristics of the host based computing model.

A client/server system has three distinct components, each focusing on a specific job a database server, a client application and a network. A server focuses on efficiently managing a resource such as database of information. The server’s primary job is to manage its resource optimally along multiple clients that concurrently request the server for the same resource.

Database servers concentrate on task such as :

Managing a single database of information among many concurrent users.

Controlling database access and other security requirements.

Protecting database information with backup and recovery features.

Centrally enforcing global data integrity rules across all client applications.

A client application is the part of the system that users employ to Interact with data. The client applications in a client/server database system focus on jobs such as

Presenting an interface a user can interact with no accomplish work.

Managing presentation logic such as popup list on a data entry form or bar graphs in a graphical data presentation tool.

Performing application logic, such as calculating fields in a data entry form.

Validating data entry.

Requesting and receiving information from a database server.

Oracle and clientserver :

Oracle is one of many database servers that we can plug into a client server equation. Oracle works to efficiently manage its resource, a database of information, among the multiple clients requesting and sending data in the network.

Features :

Oracle supports all major Operating Systems for both clients and servers, including MS-DOS, NetWare, UnixWare, OS/2 and most of the Unix flavors.

Oracle has client/server features developers can use to minimize network I/O between clients and servers.

Oracle has features that make it easy to administer complicated client/server systems.

WINDOWS 2000