How to Execute AND clause only if param is not NULL

Question

Hi,

I have a sql statement something like below but I want the AND condition to be executed only when the @param1 is not NULL, else I want all the record to be retuned for ID 123. Can you please advise on how to accomplish this task?

Declare @param1 varchar(255) = NULL
SET @param1='B1, B2'

SELECT C.* FROM Customer C
WHERE C.ID = 123
AND C.Degree IN ISNULL(@param1, C.Degree)

Answer 1

This will work in certain circumstances:

SELECT * 
FROM Customer
WHERE ID = 123
AND ( @param1 is null or Degree IN (select trim(value) from string_split(@param1, ',')) )
option (recompile)