sql of join many tables needs table Alias, while join two tables needs not

[l1t1]

create table t100(a UInt8) engine=MergeTree order by a;
insert into t100 select * from numbers(1,100);
select count(*) from t100,t100; -- OK
select count(*) from t100,t100,t100; -- FAIL

Received exception from server (version 20.6.1):
Code: 352. DB::Exception: Received from localhost:9000. DB::Exception: Ambiguous column 't100.a'.
0 rows in set. Elapsed: 0.002 sec.

select count(*) from t100,t100 a,t100 b; -- OK
select count(*) from t100,t100 a,t100 b,t100 c; -- OK

[4ertus2]

Related #4567