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pengbo d9b2ce0f0f [SPARK-27539][SQL] Fix inaccurate aggregate outputRows estimation with column containing null values 
## What changes were proposed in this pull request?
This PR is follow up of https://github.com/apache/spark/pull/24286. As gatorsmile pointed out that column with null value is inaccurate as well.

```
> select key from test;
2
NULL
1
spark-sql> desc extended test key;
col_name key
data_type int
comment NULL
min 1
max 2
num_nulls 1
distinct_count 2
```

The distinct count should be distinct_count + 1 when column contains null value.
## How was this patch tested?

Existing tests & new UT added.

Closes #24436 from pengbo/aggregation_estimation.

Authored-by: pengbo <bo.peng1019@gmail.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>
2019-04-22 20:30:08 -07:00
..
catalyst [SPARK-27539][SQL] Fix inaccurate aggregate outputRows estimation with column containing null values 2019-04-22 20:30:08 -07:00
core [SPARK-27535][SQL][TEST] Date and timestamp JSON benchmarks 2019-04-23 11:09:14 +09:00
hive [SPARK-27392][SQL] TestHive test tables should be placed in shared test state, not per session 2019-04-22 11:05:31 -07:00
hive-thriftserver [SPARK-27404][CORE][SQL][STREAMING][YARN] Fix build warnings for 3.0: postfixOps edition 2019-04-11 13:43:44 -05:00
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-27328][SQL] Add 'deprecated' in ExpressionDescription for extended usage and SQL doc 2019-04-09 13:49:42 +08:00
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.