Github user liancheng commented on the pull request:
https://github.com/apache/spark/pull/10099#issuecomment-161235263
For example, the following snippet
```scala
val path = "file:///tmp/parquet/unsafe"
(sqlContext range 10 coalesce 1).write mode "overwrite" parquet path
sqlContext.read parquet path registerTempTable "u"
sqlContext.sql("select count(*) from (select * from u where id > 3) a join
u b where a.id = b.id") explain true
```
gives the following query plan explanation, which can be (arguably) more
intuitive:
```
== Parsed Logical Plan ==
'Project [unresolvedalias((count(1),mode=Complete,isDistinct=false))]
+- 'Filter ('a.id = 'b.id)
+- 'Join Inner, None
:- 'Subquery a
: +- 'Project [unresolvedalias(*)]
: +- 'Filter ('id > 3)
: +- 'UnresolvedRelation `u`, None
+- 'UnresolvedRelation `u`, Some(b)
== Analyzed Logical Plan ==
_c0: bigint
Aggregate [(count(1),mode=Complete,isDistinct=false) AS _c0#13L]
+- Filter (id#0L = id#12L)
+- Join Inner, None
:- Subquery a
: +- Project [id#0L]
: +- Filter (id#0L > cast(3 as bigint))
: +- Subquery u
: +- Relation[id#0L]
ParquetRelation[file:/tmp/parquet/unsafe]
+- Subquery b
+- Subquery u
+- Relation[id#12L] ParquetRelation[file:/tmp/parquet/unsafe]
== Optimized Logical Plan ==
Aggregate [(count(1),mode=Complete,isDistinct=false) AS _c0#13L]
+- Project
+- Join Inner, Some((id#0L = id#12L))
:- Project [id#0L]
: +- Filter (id#0L > 3)
: +- Relation[id#0L] ParquetRelation[file:/tmp/parquet/unsafe]
+- Relation[id#12L] ParquetRelation[file:/tmp/parquet/unsafe]
== Physical Plan ==
TungstenAggregate(key=[],
functions=[(count(1),mode=Final,isDistinct=false)], output=[_c0#13L])
+- TungstenExchange SinglePartition, None
+- TungstenAggregate(key=[],
functions=[(count(1),mode=Partial,isDistinct=false)], output=[count#16L])
+- Project
+- BroadcastHashJoin [id#0L], [id#12L], BuildRight
:- Filter (id#0L > 3)
: +- Scan ParquetRelation[file:/tmp/parquet/unsafe]
PushedFilter: [GreaterThan(id,3)] [id#0L]
+- Scan ParquetRelation[file:/tmp/parquet/unsafe] PushedFilter:
[] [id#12L]
```
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