create procedure LevenshteinDistance(@string1 varchar(4000), @string2 varchar(4000))
as
begin
    set nocount on

    if (@string1 is null) Raiserror ('Строка 1 не должна быть пустой', 16, 1);
    if (@string2 is null) Raiserror ('Строка 2 не должна быть пустой', 16, 1);

	declare @diff int
	declare @len1 int
	declare @len2 int

	set @len1 = len(@string1)
	set @len2 = len(@string2)

	declare @m table (i int, j int, val int)

	declare @i int, @j int

	set @i = 0
	while (@i <= @len1)
	begin
		delete @m where i=@i and j=0

		insert into @m (i, j, val)
		values (@i, 0, @i)
		set @i = @i + 1
	end

	set @j = 0
	while (@j <= @len2)
	begin
		delete @m where i=0 and j=@j

		insert into @m (i, j, val)
		values (0, @j, @j)
		set @j = @j + 1
	end


	set @i = 1
	while (@i <= @len1) begin
		set @j = 1
		while (@j <= @len2) begin

			if (substring(@string1, @i, 1) = substring(@string2, @j, 1))
				set @diff = 0
			else
				set @diff = 1


			declare @minval int

			select @minval = min(val)
			from (
					select isnull(val, 0) + 1 as val
					from @m
					where i = @i-1 and j = @j

					union

					select isnull(val, 0) + 1 as val
					from @m
					where i = @i and j = @j-1

					union

					select isnull(val, 0) + @diff as val
					from @m
					where i = @i-1 and j = @j-1
				) t

			delete @m where i=@i and j=@j

			insert into @m (i, j, val)
			values (@i, @j, isnull(@minval, 0))

			set @j = @j + 1
		end
		set @i = @i + 1
	end

	declare @retval int
	select @retval = isnull(val, 0)
	from @m
	where i = @len1 and j = @len2

	return @retval
end