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Kevin Yu c66d64b3df [SPARK-14878][SQL] Trim characters string function support 
#### What changes were proposed in this pull request?

This PR enhances the TRIM function support in Spark SQL by allowing the specification
of trim characters set. Below is the SQL syntax :

``` SQL
<trim function> ::= TRIM <left paren> <trim operands> <right paren>
<trim operands> ::= [ [ <trim specification> ] [ <trim character set> ] FROM ] <trim source>
<trim source> ::= <character value expression>
<trim specification> ::=
  LEADING
| TRAILING
| BOTH
<trim character set> ::= <characters value expression>
```
or
``` SQL
LTRIM (source-exp [, trim-exp])
RTRIM (source-exp [, trim-exp])
```

Here are the documentation link of support of this feature by other mainstream databases.
- **Oracle:** [TRIM function](http://docs.oracle.com/cd/B28359_01/olap.111/b28126/dml_functions_2126.htm#OLADM704)
- **DB2:** [TRIM scalar function](https://www.ibm.com/support/knowledgecenter/en/SSMKHH_10.0.0/com.ibm.etools.mft.doc/ak05270_.htm)
- **MySQL:** [Trim function](http://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_trim)
- **Oracle:** [ltrim](https://docs.oracle.com/cd/B28359_01/olap.111/b28126/dml_functions_2018.htm#OLADM594)
- **DB2:** [ltrim](https://www.ibm.com/support/knowledgecenter/en/SSEPEK_11.0.0/sqlref/src/tpc/db2z_bif_ltrim.html)

This PR is to implement the above enhancement. In the implementation, the design principle is to keep the changes to the minimum. Also, the exiting trim functions (which handles a special case, i.e., trimming space characters) are kept unchanged for performane reasons.
#### How was this patch tested?

The unit test cases are added in the following files:
- UTF8StringSuite.java
- StringExpressionsSuite.scala
- sql/SQLQuerySuite.scala
- StringFunctionsSuite.scala

Author: Kevin Yu <qyu@us.ibm.com>

Closes #12646 from kevinyu98/spark-14878.
2017-09-18 12:12:35 -07:00
..
catalyst [SPARK-14878][SQL] Trim characters string function support 2017-09-18 12:12:35 -07:00
core [SPARK-14878][SQL] Trim characters string function support 2017-09-18 12:12:35 -07:00
hive [SPARK-22047][TEST] ignore HiveExternalCatalogVersionsSuite 2017-09-18 16:42:08 +08:00
hive-thriftserver [SPARK-18061][THRIFTSERVER] Add spnego auth support for ThriftServer thrift/http protocol 2017-09-06 09:39:39 +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 [SPARK-21485][SQL][DOCS] Spark SQL documentation generation for built-in functions 2017-07-26 09:38:51 -07:00

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 allows 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.