Github user dongjoon-hyun commented on the issue:
https://github.com/apache/spark/pull/14132
Oh, thank you, @cloud-fan . For current Hive, it is ignored. The followings
have the same plans.
- SELECT * FROM (SELECT * FROM t1) x, t1;
- SELECT /*+ MAPJOIN(t1) */ * FROM (SELECT * FROM t1) x, t1;
- SELECT /*+ MAPJOIN(t1) */ * FROM (SELECT * FROM t1) x, t2;
- SELECT /*+ MAPJOIN(t2) */ * FROM (SELECT * FROM t1) x, t2;
```sql
hive> set hive.auto.convert.join=false;
hive> EXPLAIN SELECT * FROM (SELECT * FROM t1) x, t1;
Warning: Shuffle Join JOIN[7][tables = [$hdt$_0, $hdt$_1]] in Stage
'Stage-1:MAPRED' is a cross product
OK
Explain
STAGE DEPENDENCIES:
Stage-1 is a root stage
Stage-0 depends on stages: Stage-1
STAGE PLANS:
Stage: Stage-1
Map Reduce
Map Operator Tree:
hive> EXPLAIN SELECT /*+ MAPJOIN(t1) */ * FROM (SELECT * FROM t1) x, t1;
Warning: Shuffle Join JOIN[5][tables = [x, t1]] in Stage 'Stage-1:MAPRED'
is a cross product
OK
Explain
STAGE DEPENDENCIES:
Stage-1 is a root stage
Stage-0 depends on stages: Stage-1
STAGE PLANS:
Stage: Stage-1
Map Reduce
Map Operator Tree:
hive> EXPLAIN SELECT /*+ MAPJOIN(t1) */ * FROM (SELECT * FROM t1) x, t2;
Warning: Shuffle Join JOIN[5][tables = [x, t2]] in Stage 'Stage-1:MAPRED'
is a cross product
OK
Explain
STAGE DEPENDENCIES:
Stage-1 is a root stage
Stage-0 depends on stages: Stage-1
STAGE PLANS:
Stage: Stage-1
Map Reduce
Map Operator Tree:
hive> EXPLAIN SELECT /*+ MAPJOIN(t2) */ * FROM (SELECT * FROM t1) x, t2;
Warning: Shuffle Join JOIN[5][tables = [x, t2]] in Stage 'Stage-1:MAPRED'
is a cross product
OK
Explain
STAGE DEPENDENCIES:
Stage-1 is a root stage
Stage-0 depends on stages: Stage-1
STAGE PLANS:
Stage: Stage-1
Map Reduce
Map Operator Tree:
```
In fact, HIVE-3784 (https://issues.apache.org/jira/browse/HIVE-3784) was
January 2013.
Here is the git commit
https://github.com/apache/hive/commit/3dca21456a34b6db9cf03e755fae8ecdfaef1730 .
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