e3201e165e
## What changes were proposed in this pull request? Add SQL support for Pivot according to Pivot grammar defined by Oracle (https://docs.oracle.com/database/121/SQLRF/img_text/pivot_clause.htm) with some simplifications, based on our existing functionality and limitations for Pivot at the backend: 1. For pivot_for_clause (https://docs.oracle.com/database/121/SQLRF/img_text/pivot_for_clause.htm), the column list form is not supported, which means the pivot column can only be one single column. 2. For pivot_in_clause (https://docs.oracle.com/database/121/SQLRF/img_text/pivot_in_clause.htm), the sub-query form and "ANY" is not supported (this is only supported by Oracle for XML anyway). 3. For pivot_in_clause, aliases for the constant values are not supported. The code changes are: 1. Add parser support for Pivot. Note that according to https://docs.oracle.com/database/121/SQLRF/statements_10002.htm#i2076542, Pivot cannot be used together with lateral views in the from clause. This restriction has been implemented in the Parser rule. 2. Infer group-by expressions: group-by expressions are not explicitly specified in SQL Pivot clause and need to be deduced based on this rule: https://docs.oracle.com/database/121/SQLRF/statements_10002.htm#CHDFAFIE, so we have to post-fix it at query analysis stage. 3. Override Pivot.resolved as "false": for the reason mentioned in [2] and the fact that output attributes change after Pivot being replaced by Project or Aggregate, we avoid resolving parent references until after Pivot has been resolved and replaced. 4. Verify aggregate expressions: only aggregate expressions with or without aliases can appear in the first part of the Pivot clause, and this check is performed as analysis stage. ## How was this patch tested? A new test suite PivotSuite is added. Author: maryannxue <maryann.xue@gmail.com> Closes #21187 from maryannxue/spark-24035. |
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Apache Spark
Spark is a fast and general cluster computing system for Big Data. It provides high-level APIs in Scala, Java, Python, and R, and an optimized engine that supports general computation graphs for data analysis. It also supports a rich set of higher-level tools including Spark SQL for SQL and DataFrames, MLlib for machine learning, GraphX for graph processing, and Spark Streaming for stream processing.
Online Documentation
You can find the latest Spark documentation, including a programming guide, on the project web page. This README file only contains basic setup instructions.
Building Spark
Spark is built using Apache Maven. To build Spark and its example programs, run:
build/mvn -DskipTests clean package
(You do not need to do this if you downloaded a pre-built package.)
You can build Spark using more than one thread by using the -T option with Maven, see "Parallel builds in Maven 3". More detailed documentation is available from the project site, at "Building Spark".
For general development tips, including info on developing Spark using an IDE, see "Useful Developer Tools".
Interactive Scala Shell
The easiest way to start using Spark is through the Scala shell:
./bin/spark-shell
Try the following command, which should return 1000:
scala> sc.parallelize(1 to 1000).count()
Interactive Python Shell
Alternatively, if you prefer Python, you can use the Python shell:
./bin/pyspark
And run the following command, which should also return 1000:
>>> sc.parallelize(range(1000)).count()
Example Programs
Spark also comes with several sample programs in the examples directory.
To run one of them, use ./bin/run-example <class> [params]. For example:
./bin/run-example SparkPi
will run the Pi example locally.
You can set the MASTER environment variable when running examples to submit
examples to a cluster. This can be a mesos:// or spark:// URL,
"yarn" to run on YARN, and "local" to run
locally with one thread, or "local[N]" to run locally with N threads. You
can also use an abbreviated class name if the class is in the examples
package. For instance:
MASTER=spark://host:7077 ./bin/run-example SparkPi
Many of the example programs print usage help if no params are given.
Running Tests
Testing first requires building Spark. Once Spark is built, tests can be run using:
./dev/run-tests
Please see the guidance on how to run tests for a module, or individual tests.
A Note About Hadoop Versions
Spark uses the Hadoop core library to talk to HDFS and other Hadoop-supported storage systems. Because the protocols have changed in different versions of Hadoop, you must build Spark against the same version that your cluster runs.
Please refer to the build documentation at "Specifying the Hadoop Version" for detailed guidance on building for a particular distribution of Hadoop, including building for particular Hive and Hive Thriftserver distributions.
Configuration
Please refer to the Configuration Guide in the online documentation for an overview on how to configure Spark.
Contributing
Please review the Contribution to Spark guide for information on how to get started contributing to the project.