with文法、再帰的な面接問題が必要です

   with CET as 

 ( 

select C1,C2,1 as l1,2 as [l2] from a where c1='A'  

    union all   

select a.*,l1+1,l2+1 from CET inner join a on CET.c2=a.c1

) 

select * from

(

select c1 as jd,l1 as [level] from cet

union

select c2,l2 as [level] from cet

)t

order by [level]