Is Number function in SQL

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create function is_numeric (
	@a varchar(100)
) returns int as begin
	declare @retval int
	set @a = replace(@a, '0', '')
	set @a = replace(@a, '1', '')
	set @a = replace(@a, '2', '')
	set @a = replace(@a, '3', '')
	set @a = replace(@a, '4', '')
	set @a = replace(@a, '5', '')
	set @a = replace(@a, '6', '')
	set @a = replace(@a, '7', '')
	set @a = replace(@a, '8', '')
	set @a = replace(@a, '9', '')
	set @a = replace(@a, '.', '')
	if len(rtrim(ltrim(@a))) > 0 set @retval = 0
	else set @retval = 1
	return @retval
end