The evolution of database systems is as follows

File Management System
Hierarchical database System
Network Database System
Relational Database System

File Management System:
The file management system also called as FMS in short is one in which all data is stored on a single large file. The main disadvantage in this system...

SQL injection is one of the security abuse in which the person makes use of SQL in other words Structured Query Language in a web form in order to have access to data and thereby make changes to the data. That is on a web application the user has to be validated with username and password and only if it matches they must gain access to the database. This is the main security action that has to be followed...

A junction record is one which allows many to many relationship between the two owner records. One of the scenario in which junction table plays a role in Microsoft Access is while creating or defining many to many relationship. Many to Many relationships between two entities are one in which one row or record of a table can relate to many records in other table and also vice-versa for the other table....

COUNT is a group function. That is which gives a result by summarizing multiple rows. All group value function will have the usage of DISTINCT or ALL option and so is the COUNT which uses the DISTINCT option. DISTINCT option is used to enforce uniqueness and this combined with COUNT is used to count only unique mentioned value.
To understand this let us see an example. Consider a table exforsys...

Tuning is one of the main function or job of a database administrator or DBA in short. This is because oracle is a relational database management system which is tunable and thus the database can be monitored and therefore appropriate measures and steps can be taken at appropriate times to increase the performance of the system. There are many reasons for performing the performance tuning in oracle....

DECODE is used to decode a CHAR or VARCHAR2 or NUMBER into any of several different character strings or numbers based on value. That is DECODE does a value-by-value substitution. For every value that is given in the DECODE function it makes an if then check and matches the value. The general format of DECODE function is given below:

DECODE(value,if1,then1,if2,then2,……,else)...

E.codd designed 12 rules that stated rules for database to be relational. These rules were named as codd’s rules. The rules are given below: 1. The Information Rule: For a database to be relational all information is represented as data values in tables. 2. The Rule of Guaranteed Access: The data represented in table by using table name, column name and primary key value defined for that table....