ERROR 1052 (23000): Column 'cnt' in order clause is ambiguous

create table o1(c char(3), y int, i int) engine=columnstore;

insert into o1 values ('abc',2016, 23), ('abc', 2016, 46), ('def', 2016, 27);

insert into o1 values ('abc',2017, 24), ('abc', 2017, 47), ('def', 2017, 28);

with c as (select y, c, count(*) cnt, sum(i) sumi from o1 group by y,c)

select

c1.y,

c1.c,

c1.cnt,

c1.sumi,

c2.y,

c2.c,

c2.cnt,

c2.sumi

from c c1, c c2

where c1.c = c2.c

and c1.y = 2016

and c2.y = 2017

order by c2.cnt;