Tuesday, 20 May 2014

Database Key

Database is a repository of any organization data. It takes data save it and provides many types of sophisticated services for record insert, update, delete, backup and many more. Here I am interested to explain many types of key.

Database : Database is a collection of related table.

Table : A Table is a collection of related records.

Record : A record is a collection of related fields

Field : A fields or attribute is a smallest individual unit of table.

NULL : NULL is a systematic approach treat blank value which is not available current but might be appear in future.

Key : Key is use to identified a record between records set.


Primary Key : Primary key is a key which is use to uniquely identified a record from set records set or table, A primary key doesn't takes NULL.

Candidate key:  A column or set of columns that can be insure unique row in the table. A candidate key is a possible primary key that is not chosen as the primary key.
Candidate key is a super key from which you cannot remove any fields.

Alter Net key : any candidate key that has not been selected as primary key it can accept NULL value  and can have duplicate value

Compound, composite, concatenated  : consist of two or more attribute