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.
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