--disable_query_log
set @@session.explicit_defaults_for_timestamp=off;
--enable_query_log
#owner: bin.lb
#owner group: sql1
#tags: group_by
#description:

--disable_warnings
drop table if exists test;
--enable_warnings
create table test(a int primary key,b int,c int);
insert into test values(1,4,null);
insert into test values(3,3,null);
insert into test values(4,3,null);
select avg(distinct(a)),avg(a),avg(b) from test;
select avg(distinct(b)),avg(b),avg(c) from test;
select avg(c),avg(b),avg(distinct(b)) from test;
select avg(c),avg(b),avg(b) from test;