DATABASE MANAGEMENT SYSTEMS AND APPLICATIONS

Essay

DATABASE MANAGEMENT SYSTEMS AND APPLICATIONS

2nd August , 2008

The first and the foremost thing to know before SQL or any other Relational Database Language can be used is what Relational Database really is . A relational database in its essence is only data gathered in an organized , predefined manner (Whatis .com , 2005 . It further on goes to say that these data items are basically arranged in a form of tables that allows data to be entered , changed , deleted in many ways . It also allows different kinds of retrieval of data through

very simple commands . It also allows creating , modifying and deleting the tables themselves

One such language that allows manipulation of the structure of the data which means the way the data has been arranged (as in , in the form of tables ) and the data itself (for example the name and age of a student in a Student database of a school ) in called the Structured Query Language (SQL . SQL has two . The SQL is used for the creation and management of the database and is being used be many Database Administrators and the End User . SQL basically involves two broad categories of Languages which includes the Data Definition Language (DDL ) and the Data Manipulation Language (DML . The DDL basically define the structure of the database which includes tables , indexes , domains and access rights of users . The basic commands included in it are the CREATE (for making new tables , index , views store procedures , ALTER (to change or modify the database or table structure to add or delete columns , change data type of columns , set , delete or change primary key or any other constraints , to rename the table ) and DROP Table (for remove tables , index , views , store procedures and the data contained in it permanently ) commands . The DDL is usually allowed to be used by a System Managers , Database Administrator or the Owner because they are used to basically define the construction , configuration , organization of the actual database . If misused by an end user or even mistakenly by the administrator , it may cause the whole database to be corrupted or execute transactions incorrectly or with Exceptional Errors . The DDL , when executed takes action and produces results immediately . One example that best serves this theory is that imagine an end user has used the DELETE TABLE command for the employee table . The next time anyone needs to retrieve , insert , update or delete any employee from that table he will receive either an error or a message that no such table exists

The DML on the other hand is most commonly used by the end users since they are the ones who are really entering , updating or deleting the data in the database either directly through the SQL commands of SELECT (to simply retrieve data from the table , index or view in a database INSERT (to add record (s ) or data item (s ) to any single table at a time UPDATE (to make any necessary changes to record (s ) or data item (s...