by Raj Kumar

Created on: October 20, 2009

Relational database is hugely popular and commercially used to store information of diverse domains including insurance, healthcare, banking, finance, automobile, manufacturing, and others. Actually a database does not works standalone but it is implemented as part of database management system. A relational database works as a part of database system called Relational Database Management System (RDBMS). This system was initially proposed by Edger Frank Codd, a British computer scientist. The relational database is based on Relational Model which follows guidelines laid down by Codd's 12 rules. In this format of data storage, user can view the data in the form of tables. A table consists of rows and columns like Microsoft Excel worksheet. Physically the actual data is stored in data pages and managed by RDBMS. Relational database use Structured Query Language (SQL) as a standard mean to access and manipulate the data in tabular form.

Depending on the data, relational database organizes it into three main relationships viz. one-to-one, one-to-many, and many-to-many. These relations are implemented by storing the data into table which in turn organize the resulting data into rows and columns. Each row in a table is related to one or more rows in another tables based on primary and foreign key relationships. Primary key is one of the database constraints which provide unique identification to each row within a table. There are other types of constraint such as check or domain constraint which is normally used to restrict the entered data or implement proper validation satisfying specific business rules. In relational model database, these constraints play important role in maintaining the entity and referential data integrity.

In relational database, SQL queries are executed to fulfill the request for data in required business format. These queries involve different operators like Comparison operators viz. =, <>, !=, <, >, >=, <= and Logical operators viz. AND, OR, NOT. These operators are used along with SQL clauses - WHERE, and HAVING clause. They provide a searching and filtering criteria for the data to be accessed or manipulated. Various commands like INSERT, UPDATE, DELETE, CREATE TABLE, and ALTER TABLE are used to play with table data. Depending on functionality, these commands are grouped into three main categories: Data Definition Language (DDL), Data Manipulation Language (DML) and Data Control Language (DCL). Several SQL joins are used to relate different tables and filter out unwanted data. These joins include SQL Equi joins, Inner join, and Outer joins. They are used along with WHERE clause in DML commands. User can create their own functions and can also use inbuilt functions like COUNT, MAX, MIN, SUM, Numerical, Date and other text functions.

Relational database involves different objects like stored procedures, views, indexes and triggers. It also provides features like SQL Tuning and Optimization for better and faster performance. Currently there are different software vendors like Microsoft, IBM, and Oracle which provide commercial RDMBS. Popular RDBMS available in the market are Microsoft SQL Server, Oracle, DB2, MySQL, ASE Sybase and many more.

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