Showing posts with label Primary Key. Show all posts
Showing posts with label Primary Key. Show all posts

Saturday, 12 April 2014

SQL Interview Questions and Answer

Clustered and Non-Clustered Index
What is an Index?
Index is a database object, which can be created on one or more columns (16 Max column combination). When creating the index will read the column(s) and forms a relevant data structure to minimize the number of data comparisons. The index will improve the performance of data retrieval.
Primary Key Constraint
A table column with this constraint is called as the key column for the table. This constraint helps the table to make sure that the value is not repeated and also no null entries. A table can have only one Primary key. Multiple columns can participate on the primary key column. Then, the uniqueness is considered among all the participant columns by combining their values.