DBMS 面试题与答案

E-R diagram also termed as Entity-Relationship diagram shows relationship between various

tables in the database.

There are three major relationship models:-

One-to-one

One-to-many

Many-to-many

There is set of rules that has been established to aid in the design of tables that are meant to be connected through relationships. This set of rules is known as Normalization.

Benefits of Normalizing your database include:

=>Avoiding repetitive entries

=>Reducing required storage space

=>Preventing the need to restructure existing tables to accommodate new data.

=>Increased speed and flexibility of queries, sorts, and summaries.

Following are the three normal forms :-

For a table to be in first normal form, data must be broken up into the smallest un possible.In addition to breaking data up into the smallest meaningful values, tables first normal form should not contain repetitions groups of fields.

The second normal form states that each field in a multiple field primary keytable must be directly related to the entire primary key. Or in other words,each non-key field should be a fact about all the fields in the primary key.

A non-key field should not depend on other Non-key field.

Denormalization is the process of putting one fact in numerous places (its vice-versa of normalization).Only one valid reason exists for denormalizing a relational design - to enhance performance.The sacrifice to performance is that you increase redundancy in database.

In fourth normal form it should not contain two or more independent multi-v about an entity and it should satisfy “Third Normal form”.

Fifth normal form deals with reconstructing information from smaller pieces of information.

These smaller pieces of information can be maintained with less redundancy.