If checks are not applied while defining and creating tables, the data stored in the tables can become redundant. For example, if you do not store the data about all the employees with complete address details, then the data would not be useful.
Similarly, if a database used by the Human Resource department stores employee contact details in two separate tables, the details of the employees might not match. This would results inconsistency and confusion.
Therefore, it is important to ensure that the data stored in tables is complete and consistent. The concept of maintaining consistency and completeness of data is called data integrity. Data integrity is enforced to ensure that the data in a database is accurate, consistent, and reliable. It is broadly classified into the following categories:
When creating tables, the SQL Server allows you to maintain integrity by:
Similarly, if a database used by the Human Resource department stores employee contact details in two separate tables, the details of the employees might not match. This would results inconsistency and confusion.
Therefore, it is important to ensure that the data stored in tables is complete and consistent. The concept of maintaining consistency and completeness of data is called data integrity. Data integrity is enforced to ensure that the data in a database is accurate, consistent, and reliable. It is broadly classified into the following categories:
- Entity integrity: ensures that each row can be uniquely identified by an attribute called the primary key column contains unique value in all the rows. In addition, this column cannot be NULL. Consider a situation where there might be two candidates for an interview with the same name ‘Jack’. By enforcing entity integrity, the two candidates can be identified by using the unique code assigned to them. For example, one candidate can have the code 001 and the other candidate can be 002.
- Domain integrity: Ensures that only a valid range of values is stored in a column. It can be enforced by restricting the type of data, the range of values, and the format of the data. For example, you have a table called Branchoffice with a column called offices are located in ‘Berkeley’, ‘Boston’, ‘Chicago’, ‘Dallas’, ‘Munchen’, ‘New Jersey’, ‘New York’, ‘Paris’, and ‘Washington’. By enforcing domain integrity, you can ensure that only valid values (as per the list specified) are entered in the City column of the BranchOffice TABLE.
- Referential integrity: Ensures that the values of the foreign key match the value of the corresponding primary key. For example, if a bicycle has been ordered and an entry is to be made in the OrderDetail table, then that bicycle code should exist in the product table. This ensures that an order is placed only for the bicycle that is available.
- User-defined integrity: Refers to a set of rules specified by a user, which do not belong to the entity, domain, and referential integrity categories.
When creating tables, the SQL Server allows you to maintain integrity by:
- Applying constraints
- Applying rules
- Using user-defined types