set hive.enforce.bucketing = true;
set hive.enforce.sorting = true;
set hive.exec.reducers.max = 1;

CREATE TABLE tbl1(key int, value string) CLUSTERED BY (key) SORTED BY (key) INTO 2 BUCKETS;
CREATE TABLE tbl2(key int, value string) CLUSTERED BY (key) SORTED BY (key) INTO 2 BUCKETS;

insert overwrite table tbl1
select * from src where key < 10;

insert overwrite table tbl2
select * from src where key < 10;

set hive.optimize.bucketmapjoin = true;
set hive.optimize.bucketmapjoin.sortedmerge = true;
set hive.input.format = org.apache.hadoop.hive.ql.io.BucketizedHiveInputFormat;

-- A join is being performed across different sub-queries, where a mapjoin is being performed in each of them.
-- Each sub-query should be converted to a sort-merge join.
-- A join followed by mapjoin is not allowed, so this query should fail.
-- Once HIVE-3403 is in, this should be automatically converted to a sort-merge join without the hint
explain
select src1.key, src1.cnt1, src2.cnt1 from
(
  select key, count(*) as cnt1 from 
  (
    select /*+mapjoin(a)*/ a.key as key, a.value as val1, b.value as val2 from tbl1 a join tbl2 b on a.key = b.key
  ) subq1 group by key
) src1
join
(
  select key, count(*) as cnt1 from 
  (
    select /*+mapjoin(a)*/ a.key as key, a.value as val1, b.value as val2 from tbl1 a join tbl2 b on a.key = b.key
  ) subq2 group by key
) src2
on src1.key = src2.key
order by src1.key, src1.cnt1, src2.cnt1;