What is the Difference between RANK() and DENSE_RANK() in SQL Server?

Rank()

Rank function will generates a unique number to each distinct row, but it leaves a gap between the groups.

Dense_Rank()

Dense_Rank function is similar to Rank with only difference, this will not leave gaps between groups.

DECLARE @Table TABLE (
      column varchar(2)
)

INSERT INTO @Table (column)
      VALUES ('A'),('A'),('A'),('B'),('B'),('C'),('C');

SELECT
      Col_Value,
      Rank() OVER (ORDER BY column) AS 'Rank',
      DENSE_RANK() OVER (ORDER BY Col_Value) AS 'DENSE_RANK'
FROM
      @Table;

Column	RANK	DENSE_RANK
A	1	1
A	1	1
A	1	1
B	4	2
B	4	2
C	6	3
C	6	3