Format a number (with commas) in SQL

CREATE FUNCTION dbo.com_FormatNumber(@value BIGINT) RETURNS VARCHAR(MAX)
AS
BEGIN
    DECLARE @minus CHAR, @working VARCHAR(MAX), @result VARCHAR(MAX), @section VARCHAR(4)
    -- First, handle the sign
    IF (@value < 0) SET @minus = '-' ELSE SET @minus = ''
    SET @working = CAST(@value AS VARCHAR)
    if (@minus <> '') SET @working = SUBSTRING(@working, 2, LEN(@working)-1)
    
    SET @result  = ''
    
	-- break apart the number into sections of 3 digits and insert commas
    WHILE LEN(@working) > 3
    BEGIN
        SET @section = ',' + SUBSTRING(@working, LEN(@working)-2, 3)
        SET @working = SUBSTRING(@working, 1, LEN(@working)-3)
        SET @result  = @section + @result
    END
    
	-- add the remaining and tack on that sign if needed
    IF (@minus <> '')
        RETURN @minus + @working + @result
        
    RETURN @working + @result
END

PRINT dbo.FormatNumber(123456)
PRINT dbo.FormatNumber(-123)

123,456
-123

Chris is the Co-founder, Administrator, Architect, Chief Editor and Shameless Hack who wrote and runs The Code Project. He's been programming since 1988 while pretending to be, in various guises, an astrophysicist, mathematician, physicist, hydrologist, geomorphologist, defence intelligence researcher and then, when all that got a bit rough on the nerves, a web developer. He is a Microsoft Visual C++ MVP both globally and for Canada locally.
 
His programming experience includes C/C++, C#, SQL, MFC, ASP, ASP.NET, and far, far too much FORTRAN. He has worked on PocketPCs, AIX mainframes, Sun workstations, and a CRAY YMP C90 behemoth but finds notebooks take up less desk space.
 
He dodges, he weaves, and he never gets enough sleep. He is kind to small animals.
 
Chris was born and bred in Australia but splits his time between Toronto and Melbourne, depending on the weather. For relaxation he is into road cycling, snowboarding, rock climbing, and storm chasing.