SQL Use Case in Where子句中的空值

Question

I have a SQL query that I am trying to incorporate the possibility of null responses in my selections.

Ultimately, this will end up in a SSRS report.

This query works fine, but any null values in p.ReferralReason will always be returned. I would like the nulls to not be returned if the value of @Reason is anything but '%':

     DECLARE @Reason varchar(100)
     SET @Reason = 'Lost To Care'


     SELECT p.Person_ID, P.Person_Name, p.ReferralReason 
     FROM VIEW_Patient p
     WHERE 
        p.ReferralReason like '%' + @Reason + '%'

I would like to incorporate all reasons with the @Reason = '%' If @Reason is set to '%', I would like to include the null values, but I do not want to include the null values if @Reason is set to anything else.

This is what I have tried, but it does not work:

     DECLARE @Reason varchar(100)
     SET @Reason = '%'


     SELECT p.Person_ID, P.Person_Name, p.ReferralReason 
     FROM VIEW_Patient p
     WHERE 
        case   
            when @Reason = '%' then (p.ReferralReason like '%' + @Reason + '%' or p.ReferralReason is null)
            else p.ReferralReason like '%' + @Reason + '%'
        end 

MS SQL Server 2008 R2.

Answer 1

If the NULL values are replaced with empty strings they will match patterns consisting entirely of % but not other strings surrounded with %

SELECT p.Person_ID,
       P.Person_Name,
       p.ReferralReason
FROM   VIEW_Patient p
WHERE  ISNULL(p.ReferralReason, '') LIKE '%' + @Reason + '%'