Merge pull request #6362 from 4ertus2/bugs

Test for crash from #5859

dbms/tests/queries/0_stateless/00980_full_join_crash_fancyqlx.reference

+1	2019-01-01	a
+1	2019-01-01	\N
+1	2019-01-01	\N
+2	2019-01-01	b
+3	2019-01-01	c

dbms/tests/queries/0_stateless/00980_full_join_crash_fancyqlx.sql

+drop table if exists test_join;
+
+create table test_join (date Date, id Int32, name Nullable(String)) engine = MergeTree partition by date order by id;
+
+insert into test_join values ('2019-01-01', 1, 'a');
+insert into test_join values ('2019-01-01', 2, 'b');
+insert into test_join values ('2019-01-01', 3, 'c');
+insert into test_join values ('2019-01-01', 1, null);
+
+SELECT id, date, name FROM (SELECT id, date, name FROM test_join GROUP BY id, name, date)
+FULL OUTER JOIN (SELECT id, date, name FROM test_join GROUP BY id, name, date)
+USING (id, name, date)
+ORDER BY id, name;
+
+drop table test_join;