SQL Server ranking functions

In SQL Server there is 4 ranking functions:

ROW_NUMBER	Returns the rank of rows within the partition of a result set, without any gaps in the ranking. The rank of a row is one plus the number of distinct ranks that come before the row in question.
RANK	Returns the rank of each row within the partition of a result set. The rank of a row is one plus the number of ranks that come before the row in question.
DENSE_RANK	Returns the rank of rows within the partition of a result set, without any gaps in the ranking. The rank of a row is one plus the number of distinct ranks that come before the row in question.
NTILE	Distributes the rows in an ordered partition into a specified number of groups. The groups are numbered, starting at one. For each row, NTILE returns the number of the group to which the row belongs.

below is the syntax:

ROW_NUMBER ( )     OVER ( [ <partition_by_clause> ] <order_by_clause> )

RANK ( )    OVER ( [ < partition_by_clause > ] < order_by_clause > )

DENSE_RANK ( )    OVER ( [ < partition_by_clause > ] < order_by_clause > ) 

NTILE (integer_expression)    OVER ( [ <partition_by_clause> ] < order_by_clause > )