xinlifoobar commented on issue #10613:
URL: https://github.com/apache/datafusion/issues/10613#issuecomment-2124136360
This is like an optimization for empty tables. The result above is when both
t3 and t4 are empty. After insert some values, the plan displayed correctly.
```sql
> insert into t3 values (1,2), (2,3)
;
+-------+
| count |
+-------+
| 2 |
+-------+
1 row(s) fetched.
Elapsed 0.004 seconds.
> explain select count(*) from ((select distinct c1, c2 from t3 order by c1
) union all (select distinct c2, c1 from t4 order by c1));
+---------------+-------------------------------------------------------------------------------------------+
| plan_type | plan
|
+---------------+-------------------------------------------------------------------------------------------+
| logical_plan | Aggregate: groupBy=[[]], aggr=[[COUNT(Int64(1)) AS
COUNT(*)]] |
| | Union
|
| | Projection:
|
| | Sort: t3.c1 ASC NULLS LAST
|
| | Projection: t3.c1
|
| | Aggregate: groupBy=[[t3.c1, t3.c2]], aggr=[[]]
|
| | TableScan: t3 projection=[c1, c2]
|
| | Projection:
|
| | Sort: t4.c1 ASC NULLS LAST
|
| | Projection: t4.c1
|
| | Aggregate: groupBy=[[t4.c2, t4.c1]], aggr=[[]]
|
| | Projection: t4.c2, t4.c1
|
| | TableScan: t4 projection=[c1, c2]
|
| physical_plan | AggregateExec: mode=Final, gby=[], aggr=[COUNT(*)]
|
| | CoalescePartitionsExec
|
| | AggregateExec: mode=Partial, gby=[], aggr=[COUNT(*)]
|
| | RepartitionExec: partitioning=RoundRobinBatch(14),
input_partitions=28 |
| | UnionExec
|
| | ProjectionExec: expr=[]
|
| | AggregateExec: mode=FinalPartitioned,
gby=[c1@0 as c1, c2@1 as c2], aggr=[] |
| | CoalesceBatchesExec: target_batch_size=8192
|
| | RepartitionExec: partitioning=Hash([c1@0,
c2@1], 14), input_partitions=14 |
| | RepartitionExec:
partitioning=RoundRobinBatch(14), input_partitions=1 |
| | AggregateExec: mode=Partial, gby=[c1@0
as c1, c2@1 as c2], aggr=[] |
| | MemoryExec: partitions=1,
partition_sizes=[1] |
| | ProjectionExec: expr=[]
|
| | AggregateExec: mode=FinalPartitioned,
gby=[c2@0 as c2, c1@1 as c1], aggr=[] |
| | CoalesceBatchesExec: target_batch_size=8192
|
| | RepartitionExec: partitioning=Hash([c2@0,
c1@1], 14), input_partitions=1 |
| | AggregateExec: mode=Partial, gby=[c2@0
as c2, c1@1 as c1], aggr=[] |
| | MemoryExec: partitions=1,
partition_sizes=[0] |
| |
|
+---------------+-------------------------------------------------------------------------------------------+
2 row(s) fetched.
Elapsed 0.018 seconds.
> select count(*) from ((select distinct c1, c2 from t3 order by c1 ) union
all (select distinct c2, c1 from t4 order by c1));
+----------+
| COUNT(*) |
+----------+
| 2 |
+----------+
1 row(s) fetched.
Elapsed 0.019 seconds.
```
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