Question

Code bellow is not working, any ideas why?

declare @Counter int set @Counter = 0 declare @ConcText nvarchar(1000)  while @Counter < 5 begin     --set @ConcText = @ConcText + cast(@Counter as nvarchar(10)) + N' counter,'     --set @ConcText = @ConcText + convert(nvarchar(10), @Counter) + N' counter,'     set @ConcText = @ConcText + N' counter,'     set @Counter = @Counter + 1 end print @ConcText --<-- this is null, why  ?? 

Answer 1

See MSDN: + (String Concatenation) (Transact-SQL):

Just like arithmetic operations that are performed on null values, when a null value is added to a known value the result is typically an unknown value, a string concatenation operation that is performed with a null value should also produce a null result.

So to get things work, it’s a good practice to initiate varchar variables immediatly after declare:

DECLARE @ConcText NVARCHAR(1000) SET @ConcText  = '' 

Other way to handle NULL concat issue (in case you don’t know if value is NULL or not) – ISNULL or COALESCE:

SET @ConcText = ISNULL(@ConcText, '') + N' counter,' SET @ConcText = COALESCE(@ConcText, '') + N' counter,'