How to calculate the sum of a value as a single digit value

DECLARE @tmp TABLE (ID INT IDENTITY(1,1), val VARCHAR(30))

INSERT INTO @tmp (val)
SELECT '1' AS val
UNION ALL SELECT '22' AS val
UNION ALL SELECT '333' AS val
UNION ALL SELECT '4444' AS val
UNION ALL SELECT '55555' AS val


SELECT val, CASE WHEN CastingOutNines=0 THEN 9 ELSE CastingOutNines END AS SumOfDigits 
FROM (
	SELECT val, ABS(CONVERT(INT, val)) % 9 AS CastingOutNines
	FROM @tmp
) AS T

val SumOfDigits
1   1
22  4
333 9
4444    7
55555   7

DECLARE @myFirstSums TABLE(ID INT, val NVARCHAR(30), SumOfDigits INT)

;WITH myValues AS
(
	SELECT ID, val, CONVERT(INT, LEFT(val,1)) AS newVal, RIGHT(val, LEN(val)-1) AS Remainder
	FROM @tmp
	WHERE LEN(val)>=1
	UNION ALL
	SELECT ID, val, CONVERT(INT, LEFT(Remainder,1)) AS newVal, RIGHT(Remainder, LEN(Remainder)-1) AS Remainder
	FROM myValues
	WHERE LEN(Remainder)>=1
	UNION ALL
	SELECT ID, val, CONVERT(INT, Remainder) AS newVal, NULL AS Remainder
	FROM myValues
	WHERE LEN(Remainder)=0
)
INSERT INTO @myFirstSums (ID, val, SumOfDigits)
SELECT ID, val, SUM(newVal) AS SumOfDigits
FROM myValues
GROUP BY ID, val
ORDER BY ID, val

;WITH mySums AS
(
	SELECT ID, val, SumOfDigits, CONVERT(INT, LEFT(CONVERT(VARCHAR(10),SumOfDigits),1)) AS newVal, RIGHT(CONVERT(VARCHAR(10),SumOfDigits), LEN(CONVERT(VARCHAR(10),SumOfDigits))-1) AS Remainder
	FROM @myFirstSums
	WHERE LEN(CONVERT(VARCHAR(10),SumOfDigits))>=1
	UNION ALL
	SELECT ID, val, SumOfDigits, CONVERT(INT, LEFT(Remainder,1)) AS newVal, RIGHT(Remainder, LEN(Remainder)-1) AS Remainder
	FROM mySums
	WHERE LEN(Remainder)>=1
	UNION ALL
	SELECT ID, val, SumOfDigits, CONVERT(INT, Remainder) AS newVal, NULL AS Remainder
	FROM mySums
	WHERE LEN(Remainder)=0
)
SELECT ID, val, SUM(newVal) AS SumOfDigits
FROM mySums
GROUP BY ID, val

DECLARE @Number INT
DECLARE @Count INT = 0
DECLARE @Count1 INT = 0
DECLARE @Intnum INT = 55
DECLARE @intFlag INT = 1

WHILE (@intFlag <= LEN(@IntNum))
BEGIN
    SET @Number = SUBSTRING(CAST(@Intnum AS VARCHAR(max)), @intFlag, 1)
    SET @Count = @Count + @Number
    SET @intFlag = @intFlag + 1
END

IF LEN(@Count) > 1
BEGIN
    DECLARE @intFlag1 INT = 1

    WHILE (LEN(@Count1) = 1)
    BEGIN
        SET @Number = SUBSTRING(CAST(@Count AS VARCHAR(max)), @intFlag1, 1)
        SET @Count1 = @Count1 + @Number
        SET @intFlag1 = @intFlag1 + 1

        IF LEN(@Count) + 1 = @intFlag1
            BREAK
        ELSE
            CONTINUE
    END
END

SELECT @Count1 AS 'Count'