or
Anonymous
I have a question about this fiddle:

<>https://dbfiddle.uk?rdbms=sqlserver_2019&fiddle=5fb4c089af3d52e645aade8970793767

Is it ever possible to get -1 as the result of this query? 
I think no, right because potato can be either null or not null and the case covers both scenario? 

sql server 11 

Sincerely, 
Top Answer
Ami
You are correct.

The CASE conditional expression can evaluate to either 1 or 0, never to a NULL.

The encapsulating ISNULL function will always see a concrete value, `1` or `0`, and so will never return `-1`.

If you explain what you are trying to achieve with this code that doesn't seem to work for you, we may be able to offer some advice.
Trying to understand an isnull expression
ypercubeᵀᴹ
@Ami I edited the answer. The isnull can return 1 or 0, whatever the case returns. It is true that it can never return -1.
Lamak replying to Anonymous
that fiddle seems to work fine?
Anonymous
https://dbfiddle.uk/?rdbms=sqlserver_2012&fiddle=d184d1b358b81986fa8b0c2abc86eae9
Anonymous
the real code is not much more complex than this. just trying to understand if I am missing something... 
Max
have you tried `set @potato = null;` and seeing what is returned?  Also, try removing the `set` statement altogether.  This seems like a pretty easy thing to prove.  If you have a more complex scenario in reality, please post that.  Cheers!