by, 03-09-2012 at 07:26 PM (375 Views)
It shall be ensured by the relational tables that data is always accessible and accurate. To do this, implementation of the integrity rules is required. These rules shall be followed.
- There shall be uniqueness in a table’s rows.
- Correct results are not found easily and accessing data might result into certain issues. This happens when duplicate rows are present.
Rules can be applied by user in most DBMS that duplicated rows are not permitted. In those cases, the insertion of the duplicated results in table would be prevented.
Other rule which is applied to the relational model is that values of the columns shall not among the repeating groups.
The 3rd rule of integrity is regarding the null value concept. A null value will be inserted by the data base when data is not present. This is done so that for indicating that the values are missing in table. Null values don’t equate to blank or zero. Two null values are not taken as equal however blank value is taken as an equal to the other blank value. On the other hand zero value is equivalent to other equal value.
1 or more than one column does the identification of particular row in case there are unique rows present in a table. Group of columns or a single column that identify row is known as primary key.
Primary key is never null. Column which is primary key’s part is also not null. This is known as entity integrity.