Explain with example ISNULL, NULLIF and COALESCE in SQL Server

ISNULL : Replaces NULL with the specified replacement value.

NULLIF : Returns a null value if the two specified expressions are equal.

COALESCE : Returns the first non-null argument.(msdn: Evaluates the arguments in order and returns the current value of the first expression that initially does not evaluate to NULL).

Here are the examples and it's results:

SELECT ISNULL(null,1)
--Result: 1

SELECT NULLIF(1,1)
--Result: NULL

SELECT COALESCE(1,null,null,null)
--Result: 1

SELECT COALESCE(null,2,3,4)
--Result: 2

SELECT COALESCE(null,null,3,4)
--Result: 3

SELECT COALESCE(null,null,null,4)
--Result: 4

SELECT ISNULL(NULLIF(COALESCE(null,null,null,4),4),1)
--Result: 1