DATABASE | ORACLE | ORACLE INTERVIEW QUESTION AND ANSWERS 9 | WHAT IS AN ORACLE INDEX? | WHAT ARE THE DIFFERENT INDEX CONFIGURATIONS A TABLE CAN HAVE? | WHAT IS DIFFERENCE BETWEEN UNIQUE CONSTRAINT AND PRIMARY KEY CONSTRAINT? | WHAT IS BCP? WHEN DOES IT USED? | HOW TO KNOW WHICH INDEX A TABLE IS USING?

Oracle Interview Question and Answers:

41.     What is an Oracle index?
      An index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

42.     What are the different index configurations a table can have?
      A table can have one of the following index configurations
    No indexes
    A clustered index
    A clustered index and many nonclustered indexes
    A nonclustered index
    Many nonclustered indexes.

43.     What is difference between UNIQUE constraint and PRIMARY KEY constraint?
      A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY can't contain Nulls. A table can have only one primary keys.

44.     What is BCP? When does it used?
      BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the structures same as source to destination.
 
45.     How to know which index a table is using?
      SELECT table_name,index_name FROM user_constraints.