WITH
 T1 AS(SELECT * FROM(VALUES(1,'а'),(2,'б'),(3,'с'))Е(f1,f2))
,T2 AS(SELECT * FROM(VALUES('a'),('b'),('c'),('d'),('e'),('f'),('g'),('h'),('i'),('j'),('k'),('l'),('m'),('n'),('o'),('p'),('q'),('r'),('s'),('t'),('u'),('v'),('w'),('x'),('y'),('z'))T(f))
SELECT T1.*,T.f
FROM T1
JOIN(SELECT N=ROW_NUMBER()OVER(ORDER BY f),* FROM T2)T ON T1.f1=(T.N-1)%3+1;