DBMS 面试题与答案

A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.

1. Partial Key: It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator. 

2. Alternate Key: All Candidate Keys excluding the Primary Key are known as Alternate Keys.

Indexing is a technique for determining how quickly specific data can be found. 

Types: 

1. Binary search style indexing 

2. B-Tree indexing 

3. Inverted list indexing 

4. Memory resident table 

5. Table indexing 

A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.

The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.