T-SQL: Best way to handle NULL values in string concatenation

You can use the Concat function in SQL 2012 and later

SELECT City, State, Country,
Concat(City, ', ', State, ', ', Country) AS 'Location'
FROM Users

Yes that is the way to go. You could also use isnull() but coalesce is more standard. You might consider if you might have nulls in city or country as well. You also might consider that users may have multipel addresses and may have more than one city, state, country and perhaps a related table would be better for this information.

To predictably look correct with commas between every two fields, you can use this form

;with users(City, State, Country) as (
select 'a', null, 'c' union all
select 'a', 'b', 'c' union all
select null, null, 'c')

-- ignore above this line
SELECT City, State, Country,
    STUFF(
        ISNULL(', ' + City, '')+
        ISNULL(', ' + State, '')+
        ISNULL(', ' + Country, ''), 1, 2, '') AS 'Location'
FROM Users

Output

City State Country Location
---- ----- ------- --------
a    NULL  c       a, c
a    b     c       a, b, c
NULL NULL  c       c