Database

SQL (Structured Query Language)-

Sql is a standard language for making quires in relational database management p-ackage, such as sql server , Oracle etc. The standard language for accessing client/server database is also SQL.This fourth generation language is a very simple and powerful language because its uses compact and performs very complex jobs to excess information from a large sized Database.

Characteristics of SQL

a)      SQL is oriented specifically around relational Database.

b)      SQL allows users to create domains as object in a schema.

c)      Privilenges can be granted or denied using SQL commands.

d)      SQL allows use of temporary tables. Temporary tables are used for storing intermediate results.

e)      SQL provides a flexible transaction management. A transaction is a group of SQL statement that success or fails as a group.

Advantage of SQL-

You can use SQL commands for the following purpose-

·         Creating, deleting, and modifying tables’ structures.

·         Inserting data into tables.

·         Updating Data. This includes maintaining data in a database, and manipulating the stored values to keep the information defined relationship.

·         Defining the relationship be3tween two or more tables.

Keys-

Each Table in a Database must have a unique identifier that consists of one or more fields. Without this unique identifiers, there is no way to retrieve a specific record from tables in a Database. There are Different types of Keys-

Primary Keys- The field or group of fields that is unique identifiers for a table called the Primary key. Primary key uniquely identifies each record in the tables and must never be the same for two records.

Composite Key- There may be some cases where a record cannot be uniquely identified by a single field. In such cases, a composite key is used. A composite key is a group of fields that uniquely identifies a record.

FOREIGN KEY- A foreign key is a field in a relational tables that matches the primary key columns of another tables. The foreign key can be used to cross-reference tables.

Relational Database management System (RDBMS)-

A relational database that allows you to group data into one and more independent tables. These tables can be related to one other using key field. Let us consider a payroll application used by the department and employee record keeping system used by the personnel department. Both applications have their master files containing many common Data fields.

Data validation- validation is the processes which ensure that all data being added or edited in the records of tables meet specific conditions. A value entered in the specific field for a new record i9s compared against the expression in the validation rule field property.

Queries- Queries are questions you ask from database. Access has powerful search capabilities. Such as enquiry can be easily put to access and you will get the answer very fast.

Relationship Between Tables- A relationship is what a keyfield established between two or more tables. The values stored in key fields are duplicated in the related tables.

            There are three types of relationship that can be established among tables. These are-

1.    One to one

2.    One to many

3.    Many to many

One-to-one- The simplest type of relationship between two tables is the one-to-one relationship. It means that for every record in one table is there a single corresponding record in another table.

One-to-many- A one to many relationship is a relationship in which a record in one table has one or more related records in another tables.one to many relationship is the most common relationship used in a relational database.

Many-to-many- In many to many relationship, a record in one table has many corresponding records in a second table and for every record in the second table, there are many corresponding records in the previous table.

Arranging information in a Database-

Arranging information in a Database management packagesfirst we have to decide exactly what we want to store as Database.A record in a Database refers to one card in the cardbox, and each field in a record refers to one piece of information on the card. Thus in a Database we may like to keep each record containg the under mentioned fields-

NAME, LOCALITY, CITY, STATE, PIN CODE.