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Dilip Biswal 10f1f19659 [SPARK-21274][SQL] Implement EXCEPT ALL clause. 
## What changes were proposed in this pull request?
Implements EXCEPT ALL clause through query rewrites using existing operators in Spark. In this PR, an internal UDTF (replicate_rows) is added to aid in preserving duplicate rows. Please refer to [Link](https://drive.google.com/open?id=1nyW0T0b_ajUduQoPgZLAsyHK8s3_dko3ulQuxaLpUXE) for the design.

**Note** This proposed UDTF is kept as a internal function that is purely used to aid with this particular rewrite to give us flexibility to change to a more generalized UDTF in future.

Input Query
``` SQL
SELECT c1 FROM ut1 EXCEPT ALL SELECT c1 FROM ut2
```
Rewritten Query
```SQL
SELECT c1
    FROM (
     SELECT replicate_rows(sum_val, c1)
       FROM (
         SELECT c1, sum_val
           FROM (
             SELECT c1, sum(vcol) AS sum_val
               FROM (
                 SELECT 1L as vcol, c1 FROM ut1
                 UNION ALL
                 SELECT -1L as vcol, c1 FROM ut2
              ) AS union_all
            GROUP BY union_all.c1
          )
        WHERE sum_val > 0
       )
   )
```

## How was this patch tested?
Added test cases in SQLQueryTestSuite, DataFrameSuite and SetOperationSuite

Author: Dilip Biswal <dbiswal@us.ibm.com>

Closes #21857 from dilipbiswal/dkb_except_all_final.
2018-07-27 13:47:33 -07:00
..
catalyst [SPARK-21274][SQL] Implement EXCEPT ALL clause. 2018-07-27 13:47:33 -07:00
core [SPARK-21274][SQL] Implement EXCEPT ALL clause. 2018-07-27 13:47:33 -07:00
hive [SPARK-24865] Remove AnalysisBarrier 2018-07-27 14:29:05 +08:00
hive-thriftserver [SPARK-24829][STS] In Spark Thrift Server, CAST AS FLOAT inconsistent with spark-shell or spark-sql 2018-07-27 13:27:17 +08:00
create-docs.sh [MINOR][DOCS] Minor doc fixes related with doc build and uses script dir in SQL doc gen script 2017-08-26 13:56:24 +09:00
gen-sql-markdown.py [SPARK-21485][FOLLOWUP][SQL][DOCS] Describes examples and arguments separately, and note/since in SQL built-in function documentation 2017-08-05 10:10:56 -07:00
mkdocs.yml [SPARK-21485][SQL][DOCS] Spark SQL documentation generation for built-in functions 2017-07-26 09:38:51 -07:00
README.md [MINOR][DOC] Fix some typos and grammar issues 2018-04-06 13:37:08 +08:00

README.md

Spark SQL

This module provides support for executing relational queries expressed in either SQL or the DataFrame/Dataset API.

Spark SQL is broken up into four subprojects:

  • Catalyst (sql/catalyst) - An implementation-agnostic framework for manipulating trees of relational operators and expressions.
  • Execution (sql/core) - A query planner / execution engine for translating Catalyst's logical query plans into Spark RDDs. This component also includes a new public interface, SQLContext, that allows users to execute SQL or LINQ statements against existing RDDs and Parquet files.
  • Hive Support (sql/hive) - Includes an extension of SQLContext called HiveContext that allows users to write queries using a subset of HiveQL and access data from a Hive Metastore using Hive SerDes. There are also wrappers that allow users to run queries that include Hive UDFs, UDAFs, and UDTFs.
  • HiveServer and CLI support (sql/hive-thriftserver) - Includes support for the SQL CLI (bin/spark-sql) and a HiveServer2 (for JDBC/ODBC) compatible server.

Running sql/create-docs.sh generates SQL documentation for built-in functions under sql/site.