/    /  SQL- Interview questions Part 6

1. What is a constraint?

Answer: Constraint can be used to specify the limit on the data type of table. It specifies only while creating or altering the table statement. Sample of constraint are.

1. Not Null.

2. Check.

3. Default.

4. Unique.

5. Primary key.

6. Foreign key.


2. What is data Integrity?

Answer: Data Integrity defines the accuracy and consistency of data stored in a database. Data Integrity can also define integrity constraints to enforce business rules on the data when it is entered into the application or database.


3. What is Auto Increment?

Answer: Auto increment keyword allows the user to create a unique number to be generated when a new record is inserted into the table. IDENTITY keyword can be used in SQL SERVER and AUTO INCREMENT keyword can be used in Oracle. Mainly this keyword can be used whenever PRIMARY KEY is used.


4. Difference between Cluster and Non-Cluster Index, Explain?

Answer: Clustered index is used for easy retrieval of data from the database by altering the way that the records are stored. In this database sorts out rows by the column which is set to be clustered index.

A nonclustered index will not alter the way it was stored but creates a complete separate object within the table. Whereas, it point back to the original table rows after searching.


5. What is Datawarehouse?

Answer: Datawarehouse is a central repository of data from multiple sources of information. Those data are consolidated, transformed and made available for the mining and online processing. It have a subset of data called Data Marts.