An index is a physical structure containing pointers to the data. Indices are created in an existing table to locate rowsmore quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name.

A clustered index is a special type of index that reorders the way records in the table are physically stored. Thereforetable can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
A non clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a non clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.

Scalar  Value Function
A Scalar-valued function in SQL Server 2012 is used to return a single value of any T-SQL data type.

 CREATE FUNCTION dbo.Calculate(@val1 int, @val2 int)  
  RETURNS int  
  AS  
  BEGIN  
  DECLARE @val3 int;  
  SELECT @val3 = @val1 + @val2;  
  RETURN @val3;  
  END  

Multi Table Value Function
1. Declare a table variable that is to be returned.
2. Must have a BEGIN/END block.
3. Inside the BEGIN/END block you need code that populates the table variable.
4. You return from the function.

 CREATE FUNCTION Util.MyMTVFunction (@Parameters INT)  
 RETURNS @FunctionResultTableVariable TABLE (N INT)  
 AS  
 BEGIN  
  INSERT INTO @FunctionResultTableVariable (N)  
  SELECT column_name1,column_name2,...  
   FROM table_name
   ORDER BY column_name ase|desc;  
  RETURN;  
 END  
 GO  

In-line Table Value Function
1. Returns a select statement – there is no table variable to mess around with, no inserts, no code blocks.

A view can be thought of as a subset of a table. It can be used for retrieving data, as well as updating or deleting rows. Rows updated or deleted in the view are updated or deleted in the table the view was created with.

SQL CREATE VIEW Syntax