TSQL Script to find the number of occurrence of characters in a string

DECLARE @String VARCHAR(20) = 'Hello how r u?'

;WITH numberCTE AS
(
 SELECT 1 AS Rn
 UNION ALL
 SELECT Rn+1 FROM numberCTE WHERE Rn<LEN(@String)
)
SELECT Character = SUBSTRING(@String,rn,1),Occurance = COUNT(SUBSTRING(@String,rn,1))
FROM numberCTE 
WHERE LEN(SUBSTRING(@String,rn,1))>0
GROUP BY SUBSTRING(@String,rn,1)

Character	Occurance
?	         1
e	         1
h	         2
l	         2
o	         2
r	         1
u	         1
w	         1