Instead of shipping just the name and then looking up the info on the workers, we now ship the whole classname. Also, I refactored the file as it was getting pretty large to move out the type conversion code to its own file.
Author: Michael Armbrust <michael@databricks.com>
Closes#1552 from marmbrus/fixTempUdfs and squashes the following commits:
b695904 [Michael Armbrust] Make add jar execute with Hive. Ship the whole function class name since sometimes we cannot lookup temporary functions on the workers.
This change adds an analyzer rule to
1. find expressions in `HAVING` clause filters that depend on unresolved attributes,
2. push these expressions down to the underlying aggregates, and then
3. project them away above the filter.
It also enables the `HAVING` queries in the Hive compatibility suite.
Author: William Benton <willb@redhat.com>
Closes#1497 from willb/spark-2226 and squashes the following commits:
92c9a93 [William Benton] Removed unnecessary import
f1d4f34 [William Benton] Cleanups missed in prior commit
0e1624f [William Benton] Incorporated suggestions from @marmbrus; thanks!
541d4ee [William Benton] Cleanups from review
5a12647 [William Benton] Explanatory comments and stylistic cleanups.
c7f2b2c [William Benton] Whitelist HAVING queries.
29a26e3 [William Benton] Added rule to handle unresolved attributes in HAVING clauses (SPARK-2226)
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1491 from ueshin/issues/SPARK-2588 and squashes the following commits:
43d0a46 [Takuya UESHIN] Merge branch 'master' into issues/SPARK-2588
1023ea0 [Takuya UESHIN] Modify tests to use DSLs.
2310bf1 [Takuya UESHIN] Add some more DSLs.
Currently, the "==" in HiveQL expression will cause exception thrown, this patch will fix it.
Author: Cheng Hao <hao.cheng@intel.com>
Closes#1522 from chenghao-intel/equal and squashes the following commits:
f62a0ff [Cheng Hao] Add == Support for HiveQl
We need to use the analyzed attributes otherwise we end up with a tree that will never resolve.
Author: Michael Armbrust <michael@databricks.com>
Closes#1470 from marmbrus/fixApplySchema and squashes the following commits:
f968195 [Michael Armbrust] Use analyzed attributes when applying the schema.
4969015 [Michael Armbrust] Add test case.
Result may not be returned in the expected order, so relax that constraint.
Author: Aaron Davidson <aaron@databricks.com>
Closes#1514 from aarondav/flakey and squashes the following commits:
e5af823 [Aaron Davidson] Fix flakey HiveQuerySuite test
Author: Cheng Hao <hao.cheng@intel.com>
Closes#1436 from chenghao-intel/unwrapdata and squashes the following commits:
34cc21a [Cheng Hao] update the table scan accodringly since the unwrapData function changed
afc39da [Cheng Hao] Polish the code
39d6475 [Cheng Hao] Add HiveDecimal & HiveVarchar support in unwrap data
`StringComparison` expressions including `null` literal cases could be added to `NullPropagation`.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1451 from ueshin/issues/SPARK-2535 and squashes the following commits:
e99c237 [Takuya UESHIN] Add some tests.
8f9b984 [Takuya UESHIN] Add StringComparison case to NullPropagation.
This is a follow-up of #1428.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1432 from ueshin/issues/SPARK-2518 and squashes the following commits:
37d1ace [Takuya UESHIN] Fix foldability of Substring expression.
Moved couple rules out of NullPropagation and added more comments.
Author: Reynold Xin <rxin@apache.org>
Closes#1430 from rxin/sql-folding-rule and squashes the following commits:
7f9a197 [Reynold Xin] Updated documentation for ConstantFolding.
7f8cf61 [Reynold Xin] [SQL] Cleaned up ConstantFolding slightly.
JIRA: https://issues.apache.org/jira/browse/SPARK-2525.
Author: Yin Huai <huai@cse.ohio-state.edu>
Closes#1444 from yhuai/SPARK-2517 and squashes the following commits:
edbac3f [Yin Huai] Removed some compiler type erasure warnings.
JIRA issue: [SPARK-2119](https://issues.apache.org/jira/browse/SPARK-2119)
Essentially this PR fixed three issues to gain much better performance when reading large Parquet file off S3.
1. When reading the schema, fetching Parquet metadata from a part-file rather than the `_metadata` file
The `_metadata` file contains metadata of all row groups, and can be very large if there are many row groups. Since schema information and row group metadata are coupled within a single Thrift object, we have to read the whole `_metadata` to fetch the schema. On the other hand, schema is replicated among footers of all part-files, which are fairly small.
1. Only add the root directory of the Parquet file rather than all the part-files to input paths
HDFS API can automatically filter out all hidden files and underscore files (`_SUCCESS` & `_metadata`), there's no need to filter out all part-files and add them individually to input paths. What make it much worse is that, `FileInputFormat.listStatus()` calls `FileSystem.globStatus()` on each individual input path sequentially, each results a blocking remote S3 HTTP request.
1. Worked around [PARQUET-16](https://issues.apache.org/jira/browse/PARQUET-16)
Essentially PARQUET-16 is similar to the above issue, and results lots of sequential `FileSystem.getFileStatus()` calls, which are further translated into a bunch of remote S3 HTTP requests.
`FilteringParquetRowInputFormat` should be cleaned up once PARQUET-16 is fixed.
Below is the micro benchmark result. The dataset used is a S3 Parquet file consists of 3,793 partitions, about 110MB per partition in average. The benchmark is done with a 9-node AWS cluster.
- Creating a Parquet `SchemaRDD` (Parquet schema is fetched)
```scala
val tweets = parquetFile(uri)
```
- Before: 17.80s
- After: 8.61s
- Fetching partition information
```scala
tweets.getPartitions
```
- Before: 700.87s
- After: 21.47s
- Counting the whole file (both steps above are executed altogether)
```scala
parquetFile(uri).count()
```
- Before: ??? (haven't test yet)
- After: 53.26s
Author: Cheng Lian <lian.cs.zju@gmail.com>
Closes#1370 from liancheng/faster-parquet and squashes the following commits:
94a2821 [Cheng Lian] Added comments about schema consistency
d2c4417 [Cheng Lian] Worked around PARQUET-16 to improve Parquet performance
1c0d1b9 [Cheng Lian] Accelerated Parquet schema retrieving
5bd3d29 [Cheng Lian] Fixed Parquet log level
This is a follow-up of #1359 with nullability narrowing.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1426 from ueshin/issues/SPARK-2504 and squashes the following commits:
5157832 [Takuya UESHIN] Remove unnecessary white spaces.
80958ac [Takuya UESHIN] Fix nullability of Substring expression.
`Substring` including `null` literal cases could be added to `NullPropagation`.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1428 from ueshin/issues/SPARK-2509 and squashes the following commits:
d9eb85f [Takuya UESHIN] Add Substring cases to NullPropagation.
Author: Aaron Staple <aaron.staple@gmail.com>
Closes#1421 from staple/SPARK-2314 and squashes the following commits:
73e04dc [Aaron Staple] [SPARK-2314] Override collect and take in JavaSchemaRDD, forwarding to SchemaRDD implementations.
JIRA ticket: https://issues.apache.org/jira/browse/SPARK-2498
Author: Zongheng Yang <zongheng.y@gmail.com>
Closes#1423 from concretevitamin/scala-ref-catalyst and squashes the following commits:
325a149 [Zongheng Yang] Synchronize on a lock when initializing data type objects in Catalyst.
Author: Michael Armbrust <michael@databricks.com>
Closes#1414 from marmbrus/exprIdResolution and squashes the following commits:
97b47bc [Michael Armbrust] Attribute equality comparisons should be done by exprId.
This replaces the Hive UDF for SUBSTR(ING) with an implementation in Catalyst
and adds tests to verify correct operation.
Author: William Benton <willb@redhat.com>
Closes#1359 from willb/internalSqlSubstring and squashes the following commits:
ccedc47 [William Benton] Fixed too-long line.
a30a037 [William Benton] replace view bounds with implicit parameters
ec35c80 [William Benton] Adds fixes from review:
4f3bfdb [William Benton] Added internal implementation of SQL SUBSTR()
Please refer to JIRA (https://issues.apache.org/jira/browse/SPARK-2474) for how to reproduce the problem and my understanding of the root cause.
Author: Yin Huai <huai@cse.ohio-state.edu>
Closes#1406 from yhuai/SPARK-2474 and squashes the following commits:
96b1627 [Yin Huai] Merge remote-tracking branch 'upstream/master' into SPARK-2474
af36d65 [Yin Huai] Fix comment.
be86ba9 [Yin Huai] Correct SQL console settings.
c43ad00 [Yin Huai] Wrap the relation in a Subquery named by the table name in OverrideCatalog.lookupRelation.
a5c2145 [Yin Huai] Support sql/console.
Author: Michael Armbrust <michael@databricks.com>
Closes#1396 from marmbrus/moreTests and squashes the following commits:
6660b60 [Michael Armbrust] Blacklist a test that requires DFS command.
8b6001c [Michael Armbrust] Add golden files.
ccd8f97 [Michael Armbrust] Whitelist more tests.
Author: Michael Armbrust <michael@databricks.com>
Closes#1411 from marmbrus/nestedRepeated and squashes the following commits:
044fa09 [Michael Armbrust] Fix parsing of repeated, nested data access.
Note that this commit changes the semantics when loading in data that was created with prior versions of Spark SQL. Before, we were writing out strings as Binary data without adding any other annotations. Thus, when data is read in from prior versions, data that was StringType will now become BinaryType. Users that need strings can CAST that column to a String. It was decided that while this breaks compatibility, it does make us compatible with other systems (Hive, Thrift, etc) and adds support for Binary data, so this is the right decision long term.
To support `BinaryType`, the following changes are needed:
- Make `StringType` use `OriginalType.UTF8`
- Add `BinaryType` using `PrimitiveTypeName.BINARY` without `OriginalType`
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1373 from ueshin/issues/SPARK-2446 and squashes the following commits:
ecacb92 [Takuya UESHIN] Add BinaryType support to Parquet I/O.
616e04a [Takuya UESHIN] Make StringType use OriginalType.UTF8.
This fix obtains a comparable performance boost as [PR #1390](https://github.com/apache/spark/pull/1390) by moving an array update and deserializer initialization out of a potentially very long loop. Suggested by yhuai. The below results are updated for this fix.
## Benchmarks
Generated a local text file with 10M rows of simple key-value pairs. The data is loaded as a table through Hive. Results are obtained on my local machine using hive/console.
Without the fix:
Type | Non-partitioned | Partitioned (1 part)
------------ | ------------ | -------------
First run | 9.52s end-to-end (1.64s Spark job) | 36.6s (28.3s)
Stablized runs | 1.21s (1.18s) | 27.6s (27.5s)
With this fix:
Type | Non-partitioned | Partitioned (1 part)
------------ | ------------ | -------------
First run | 9.57s (1.46s) | 11.0s (1.69s)
Stablized runs | 1.13s (1.10s) | 1.23s (1.19s)
Author: Zongheng Yang <zongheng.y@gmail.com>
Closes#1408 from concretevitamin/slow-read-2 and squashes the following commits:
d86e437 [Zongheng Yang] Move update & initialization out of potentially long loop.
Reuse byte buffers when creating unique attributes for multiple instances of an InMemoryRelation in a single query plan.
Author: Michael Armbrust <michael@databricks.com>
Closes#1332 from marmbrus/doubleCache and squashes the following commits:
4a19609 [Michael Armbrust] Clean up concurrency story by calculating buffersn the constructor.
b39c931 [Michael Armbrust] Allocations are kind of a side effect.
f67eff7 [Michael Armbrust] Reusue same byte buffers when creating new instance of InMemoryRelation
Author: Michael Armbrust <michael@databricks.com>
Closes#1366 from marmbrus/partialDistinct and squashes the following commits:
12a31ab [Michael Armbrust] Add more efficient distinct operator.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1355 from ueshin/issues/SPARK-2428 and squashes the following commits:
b6fa264 [Takuya UESHIN] Add except and intersect methods to SchemaRDD.
`RowWriteSupport` doesn't write empty `ArrayType` value, so the read value becomes `null`.
It should write empty `ArrayType` value as it is.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1339 from ueshin/issues/SPARK-2415 and squashes the following commits:
32afc87 [Takuya UESHIN] Merge branch 'master' into issues/SPARK-2415
2f05196 [Takuya UESHIN] Fix RowWriteSupport to handle empty ArrayType correctly.
Refine `StringComparison` and related codes as follows:
- `StringComparison` could be similar to `StringRegexExpression` or `CaseConversionExpression`.
- Nullability of `StringRegexExpression` could depend on children's nullabilities.
- Add a case that the like condition includes no wildcard to `LikeSimplification`.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1357 from ueshin/issues/SPARK-2431 and squashes the following commits:
77766f5 [Takuya UESHIN] Add a case that the like condition includes no wildcard to LikeSimplification.
b9da9d2 [Takuya UESHIN] Fix nullability of StringRegexExpression.
680bb72 [Takuya UESHIN] Refine StringComparison.
Patch introduces the new way of working also retaining the existing ways of doing things.
For example build instruction for yarn in maven is
`mvn -Pyarn -PHadoop2.2 clean package -DskipTests`
in sbt it can become
`MAVEN_PROFILES="yarn, hadoop-2.2" sbt/sbt clean assembly`
Also supports
`sbt/sbt -Pyarn -Phadoop-2.2 -Dhadoop.version=2.2.0 clean assembly`
Author: Prashant Sharma <prashant.s@imaginea.com>
Author: Patrick Wendell <pwendell@gmail.com>
Closes#772 from ScrapCodes/sbt-maven and squashes the following commits:
a8ac951 [Prashant Sharma] Updated sbt version.
62b09bb [Prashant Sharma] Improvements.
fa6221d [Prashant Sharma] Excluding sql from mima
4b8875e [Prashant Sharma] Sbt assembly no longer builds tools by default.
72651ca [Prashant Sharma] Addresses code reivew comments.
acab73d [Prashant Sharma] Revert "Small fix to run-examples script."
ac4312c [Prashant Sharma] Revert "minor fix"
6af91ac [Prashant Sharma] Ported oldDeps back. + fixes issues with prev commit.
65cf06c [Prashant Sharma] Servelet API jars mess up with the other servlet jars on the class path.
446768e [Prashant Sharma] minor fix
89b9777 [Prashant Sharma] Merge conflicts
d0a02f2 [Prashant Sharma] Bumped up pom versions, Since the build now depends on pom it is better updated there. + general cleanups.
dccc8ac [Prashant Sharma] updated mima to check against 1.0
a49c61b [Prashant Sharma] Fix for tools jar
a2f5ae1 [Prashant Sharma] Fixes a bug in dependencies.
cf88758 [Prashant Sharma] cleanup
9439ea3 [Prashant Sharma] Small fix to run-examples script.
96cea1f [Prashant Sharma] SPARK-1776 Have Spark's SBT build read dependencies from Maven.
36efa62 [Patrick Wendell] Set project name in pom files and added eclipse/intellij plugins.
4973dbd [Patrick Wendell] Example build using pom reader.
Author: Reynold Xin <rxin@apache.org>
Closes#1334 from rxin/sqlConfThreadSafetuy and squashes the following commits:
c1e0a5a [Reynold Xin] Fixed the duplicate comment.
7614372 [Reynold Xin] [SPARK-2409] Make SQLConf thread safe.
Author: Michael Armbrust <michael@databricks.com>
Closes#1325 from marmbrus/slowLike and squashes the following commits:
023c3eb [Michael Armbrust] add comment.
8b421c2 [Michael Armbrust] Handle the case where the final % is actually escaped.
d34d37e [Michael Armbrust] add periods.
3bbf35f [Michael Armbrust] Roll back changes to SparkBuild
53894b1 [Michael Armbrust] Fix grammar.
4094462 [Michael Armbrust] Fix grammar.
6d3d0a0 [Michael Armbrust] Optimize common LIKE patterns.
Using Spark's take can result in an entire in-memory partition to be shipped in order to retrieve a single row.
Author: Michael Armbrust <michael@databricks.com>
Closes#1318 from marmbrus/takeLimit and squashes the following commits:
77289a5 [Michael Armbrust] Update scala doc
32f0674 [Michael Armbrust] Custom take implementation for LIMIT queries.
Author: witgo <witgo@qq.com>
Closes#1153 from witgo/expectResult and squashes the following commits:
97541d8 [witgo] merge master
ead26e7 [witgo] Resolve sbt warnings during build
Hi all,
I want to submit a basic operator Intersect
For example , in sql case
select * from table1
intersect
select * from table2
So ,i want use this operator support this function in Spark SQL
This operator will return the the intersection of SparkPlan child table RDD .
JIRA:https://issues.apache.org/jira/browse/SPARK-2235
Author: Yanjie Gao <gaoyanjie55@163.com>
Author: YanjieGao <396154235@qq.com>
Closes#1150 from YanjieGao/patch-5 and squashes the following commits:
4629afe [YanjieGao] reformat the code
bdc2ac0 [YanjieGao] reformat the code as Michael's suggestion
3b29ad6 [YanjieGao] Merge remote branch 'upstream/master' into patch-5
1cfbfe6 [YanjieGao] refomat some files
ea78f33 [YanjieGao] resolve conflict and add annotation on basicOperator and remove HiveQl
0c7cca5 [YanjieGao] modify format problem
a802ca8 [YanjieGao] Merge remote branch 'upstream/master' into patch-5
5e374c7 [YanjieGao] resolve conflict in SparkStrategies and basicOperator
f7961f6 [Yanjie Gao] update the line less than
bdc4a05 [Yanjie Gao] Update basicOperators.scala
0b49837 [Yanjie Gao] delete the annotation
f1288b4 [Yanjie Gao] delete annotation
e2b64be [Yanjie Gao] Update basicOperators.scala
4dd453e [Yanjie Gao] Update SQLQuerySuite.scala
790765d [Yanjie Gao] Update SparkStrategies.scala
ac73e60 [Yanjie Gao] Update basicOperators.scala
d4ac5e5 [Yanjie Gao] Update HiveQl.scala
61e88e7 [Yanjie Gao] Update SqlParser.scala
469f099 [Yanjie Gao] Update basicOperators.scala
e5bff61 [Yanjie Gao] Spark SQL basicOperator add Intersect operator
For example, for
```
{"array": [{"field":214748364700}, {"field":1}]}
```
the type of field is resolved as IntType. While, for
```
{"array": [{"field":1}, {"field":214748364700}]}
```
the type of field is resolved as LongType.
JIRA: https://issues.apache.org/jira/browse/SPARK-2375
Author: Yin Huai <huaiyin.thu@gmail.com>
Closes#1308 from yhuai/SPARK-2375 and squashes the following commits:
3e2e312 [Yin Huai] Update unit test.
1b2ff9f [Yin Huai] Merge remote-tracking branch 'upstream/master' into SPARK-2375
10794eb [Yin Huai] Correctly resolve the type of a field inside an array of structs.
When execute `saveAsParquetFile` with non-primitive type, `RowWriteSupport` uses wrong type `Int` for `ByteType` and `ShortType`.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1315 from ueshin/issues/SPARK-2386 and squashes the following commits:
20d89ec [Takuya UESHIN] Use None instead of null.
bd88741 [Takuya UESHIN] Add a test.
323d1d2 [Takuya UESHIN] Modify RowWriteSupport to use the exact types to cast.
Reported by http://apache-spark-user-list.1001560.n3.nabble.com/Spark-SQL-Join-throws-exception-td8599.html
After we get the table from the catalog, because the table has an alias, we will temporarily insert a Subquery. Then, we convert the table alias to lower case no matter if the parser is case sensitive or not.
To see the issue ...
```
val sqlContext = new org.apache.spark.sql.SQLContext(sc)
import sqlContext.createSchemaRDD
case class Person(name: String, age: Int)
val people = sc.textFile("examples/src/main/resources/people.txt").map(_.split(",")).map(p => Person(p(0), p(1).trim.toInt))
people.registerAsTable("people")
sqlContext.sql("select PEOPLE.name from people PEOPLE")
```
The plan is ...
```
== Query Plan ==
Project ['PEOPLE.name]
ExistingRdd [name#0,age#1], MapPartitionsRDD[4] at mapPartitions at basicOperators.scala:176
```
You can find that `PEOPLE.name` is not resolved.
This PR introduces three changes.
1. If a table has an alias, the catalog will not lowercase the alias. If a lowercase alias is needed, the analyzer will do the work.
2. A catalog has a new val caseSensitive that indicates if this catalog is case sensitive or not. For example, a SimpleCatalog is case sensitive, but
3. Corresponding unit tests.
With this PR, case sensitivity of database names and table names is handled by the catalog. Case sensitivity of other identifiers are handled by the analyzer.
JIRA: https://issues.apache.org/jira/browse/SPARK-2339
Author: Yin Huai <huai@cse.ohio-state.edu>
Closes#1317 from yhuai/SPARK-2339 and squashes the following commits:
12d8006 [Yin Huai] Handling case sensitivity correctly. This patch introduces three changes. 1. If a table has an alias, the catalog will not lowercase the alias. If a lowercase alias is needed, the analyzer will do the work. 2. A catalog has a new val caseSensitive that indicates if this catalog is case sensitive or not. For example, a SimpleCatalog is case sensitive, but 3. Corresponding unit tests. With this patch, case sensitivity of database names and table names is handled by the catalog. Case sensitivity of other identifiers is handled by the analyzer.
Fix nullabilities of `Join`/`Generate`/`Aggregate` because:
- Output attributes of opposite side of `OuterJoin` should be nullable.
- Output attributes of generater side of `Generate` should be nullable if `join` is `true` and `outer` is `true`.
- `AttributeReference` of `computedAggregates` of `Aggregate` should be the same as `aggregateExpression`'s.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1266 from ueshin/issues/SPARK-2327 and squashes the following commits:
3ace83a [Takuya UESHIN] Add withNullability to Attribute and use it to change nullabilities.
df1ae53 [Takuya UESHIN] Modify nullabilize to leave attribute if not resolved.
799ce56 [Takuya UESHIN] Add nullabilization to Generate of SparkPlan.
a0fc9bc [Takuya UESHIN] Fix scalastyle errors.
0e31e37 [Takuya UESHIN] Fix Aggregate resultAttribute nullabilities.
09532ec [Takuya UESHIN] Fix Generate output nullabilities.
f20f196 [Takuya UESHIN] Fix Join output nullabilities.
The right side of `LeftSemi` join needs columns only used in join condition.
Author: Takuya UESHIN <ueshin@happy-camper.st>
Closes#1301 from ueshin/issues/SPARK-2366 and squashes the following commits:
7677a39 [Takuya UESHIN] Update comments.
786d3a0 [Takuya UESHIN] Rename method name.
e0957b1 [Takuya UESHIN] Add column pruning for the right side of LeftSemi join.
Author: Michael Armbrust <michael@databricks.com>
Closes#1305 from marmbrus/usePrunerPartitions and squashes the following commits:
744aa20 [Michael Armbrust] Use getAllPartitionsForPruner instead of getPartitions, which avoids retrieving auth data
This replaces #1263 with a test case.
Author: Reynold Xin <rxin@apache.org>
Author: Michael Armbrust <michael@databricks.com>
Closes#1265 from rxin/sql-analysis-error and squashes the following commits:
a639e01 [Reynold Xin] Added a test case for unresolved attribute analysis.
7371e1b [Reynold Xin] Merge pull request #1263 from marmbrus/analysisChecks
448c088 [Michael Armbrust] Add analysis checks
This is a fix for the problem revealed by PR #1265.
Currently `HiveComparisonSuite` ignores output of `ExplainCommand` since Catalyst query plan is quite different from Hive query plan. But exceptions throw from `CheckResolution` still breaks test cases. This PR catches any `TreeNodeException` and reports it as part of the query explanation.
After merging this PR, PR #1265 can also be merged safely.
For a normal query:
```
scala> hql("explain select key from src").foreach(println)
...
[Physical execution plan:]
[HiveTableScan [key#9], (MetastoreRelation default, src, None), None]
```
For a wrong query with unresolved attribute(s):
```
scala> hql("explain select kay from src").foreach(println)
...
[Error occurred during query planning: ]
[Unresolved attributes: 'kay, tree:]
[Project ['kay]]
[ LowerCaseSchema ]
[ MetastoreRelation default, src, None]
```
Author: Cheng Lian <lian.cs.zju@gmail.com>
Closes#1294 from liancheng/safe-explain and squashes the following commits:
4318911 [Cheng Lian] Don't throw TreeNodeException in `execution.ExplainCommand`
