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Interview Questions Part-1 | What is Normalization | What is De Normalization | What is a Stored Procedure | What is a Trigger in SQL Server

Oct 5, 2011
What is Normalization? 

In relational database design, the process of organizing data to minimize redundancy. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.There are three main normal forms, each with increasing levels of normalization:

  • First Normal Form (1NF): Each field in a table contains different information. For example, in an employee list, each table would contain only one birthdate field.
  • Second Normal Form (2NF): Each field in a table that is not a determiner of the contents of another field must itself be a function of the other fields in the table.
  • Third Normal Form (3NF): No duplicate information is permitted. So, for example, if two tables both require a birthdate field, the birthdate information would be separated into a separate table, and the two other tables would then access the birthdate information via an index field in the birthdate table. Any change to a birthdate would automatically be reflecting in all tables that link to the birthdate table.
There are additional normalization levels, such as Boyce Codd Normal Form (BCNF), fourth normal form (4NF) and fifth normal form (5NF). While normalization makes databases more efficient to maintain, they can also make them more complex because data is separated into so many different tables.

(2) In data processing, a process applied to all data in a set that produces a specific statistical property. For example, each expenditure for a month can be divided by the total of all expenditures to produce a percentage.

(3) In programming, changing the format of a floating-point number so the left-most digit in the mantissa is not a zero.

What is De-normalization?             

As the name indicates, de-normalization is the reverse process of normalization. It’s the controlled introduction of redundancy in to the database design.
It helps improve the query performance as the number of joins could be reduced.

What is a Stored Procedure?

Stored Procedure is a group of sql statements that has been created once and stored in server database. Stored procedures will accept input parameters so that single stored procedure can be used over network by multiple clients using different input data. Stored procedures will reduce network traffic and increase the performance. (Read more Here)

What is a Trigger?

Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table.

In SQL Server 6.5 you could define only 3 triggers per table, one for INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this restriction is gone, and you could create multiple triggers per each action. But in 7.0 there’s no way to control the order in which the triggers fire. In SQL Server 2000 you could specify which trigger fires first or fires last using sp_settriggerorder

Triggers can’t be invoked on demand. They get triggered only when an associated action (INSERT, UPDATE, and DELETE) happens on the table on which they are defined.

Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster.

Till SQL Server 7.0, triggers fire only after the data modification operation happens. So in a way, they are called post triggers. But in SQL Server 2000 you could create pre triggers also.

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