SqlServer Substring

DECLARE @strString VARCHAR(50)
SET @strString = 'SUBSTRING'

SELECT SUBSTRING(@strString,1,1) AS STRSTRING
Result:S

SELECT SUBSTRING(@strString,1,2) AS STRSTRING
Result:SU

SELECT SUBSTRING(@strString,1,3) AS STRSTRING
Result:SUB

SELECT SUBSTRING(@strString,1,4) AS STRSTRING
Result:SUBS

SELECT SUBSTRING(@strString,1,5) AS STRSTRING
Result:SUBST

SELECT SUBSTRING(@strString,1,6) AS STRSTRING
Result:SUBSTR

SELECT SUBSTRING(@strString,1,7) AS STRSTRING
Result:SUBSTRI

SELECT SUBSTRING(@strString,1,8) AS STRSTRING
Result:SUBSTRIN

SELECT SUBSTRING(@strString,1,9) AS STRSTRING
Result:SUBSTRING

SELECT SUBSTRING(@strString,3,9) AS STRSTRING
Result:BSTRING
SELECT SUBSTRING(@strString,-5,9) AS STRSTRING
Result: SUB

SELECT SUBSTRING(@strString,-7,9) AS STRSTRING
Result:S