What will be the output of the below TSQL Script?

DECLARE @String VARCHAR(MAX)
SET @String = 'DNF'

;WITH numberCTE AS
(
SELECT 1 AS Rn
UNION ALL
SELECT Rn+1 FROM numberCTE WHERE Rn<LEN(@String)
)
SELECT Characters = SUBSTRING(@String,rn,1)
FROM numberCTE

String DNF will be split into individual characters like D N F row wise.
The numberCTE generates the sequential numbers based on the length of the string. It will be 3 here.

The substring function

SUBSTRING(@String,rn,1)

will accept the numbers one by one and will return individual characters based on the Rn value.

final output

Characters

-------------

D

N

F