Quick note on NULLS: NULL means “Unknown Value”, not “0”. So adding a value to NULL results in NULL:
1 + NULL = NULL
Because NULL means “I Don't Know”, adding two NULLS together does not equate to the same value; it's still two indeterminate values.
NULL + NULL != NULL
You can work around this in T-SQL by using COALESCE.
declare @i VARCHAR(8) = NULL declare @j VARCHAR(8) = NULL SELECT @i SELECT @i + 'bob' SELECT COALESCE (@i, 'bob') if @i = @j select 'yes' else select 'no'