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Yuming Wang 0768fad777 [SPARK-28126][SQL] Support TRIM(trimStr FROM str) syntax 
## What changes were proposed in this pull request?
[PostgreSQL](7c850320d8/src/test/regress/sql/strings.sql (L624)) support  another trim pattern: `TRIM(trimStr FROM str)`:

Function | Return Type | Description | Example | Result
--- | --- | --- | --- | ---
trim([leading \| trailing \| both] [characters] from string) | text | Remove the longest string containing only characters from characters (a space by default) from the start, end, or both ends (both is the default) of string | trim(both 'xyz' from 'yxTomxx') | Tom

This pr add support this trim pattern. After this pr. We can support all standard syntax except `TRIM(FROM str)` because it conflicts with our Literals:
```sql
Literals of type 'FROM' are currently not supported.(line 1, pos 12)

== SQL ==
SELECT TRIM(FROM ' SPARK SQL ')
```

PostgreSQL, Vertica and MySQL support this pattern. Teradata, Oracle, DB2, SQL Server, Hive and Presto
**PostgreSQL**:
```
postgres=# SELECT substr(version(), 0, 16), trim('xyz' FROM 'yxTomxx');
     substr      | btrim
-----------------+-------
 PostgreSQL 11.3 | Tom
(1 row)
```
**Vertica**:
```
dbadmin=> SELECT version(), trim('xyz' FROM 'yxTomxx');
              version               | btrim
------------------------------------+-------
 Vertica Analytic Database v9.1.1-0 | Tom
(1 row)
```
**MySQL**:
```
mysql> SELECT version(), trim('xyz' FROM 'yxTomxx');
+-----------+----------------------------+
| version() | trim('xyz' FROM 'yxTomxx') |
+-----------+----------------------------+
| 5.7.26    | yxTomxx                    |
+-----------+----------------------------+
1 row in set (0.00 sec)
```

More details:
https://www.postgresql.org/docs/11/functions-string.html

## How was this patch tested?

unit tests

Closes #24924 from wangyum/SPARK-28075-2.

Authored-by: Yuming Wang <yumwang@ebay.com>
Signed-off-by: gatorsmile <gatorsmile@gmail.com>
2019-06-22 23:10:09 -07:00
..
catalyst [SPARK-28126][SQL] Support TRIM(trimStr FROM str) syntax 2019-06-22 23:10:09 -07:00
core [SPARK-28126][SQL] Support TRIM(trimStr FROM str) syntax 2019-06-22 23:10:09 -07:00
hive [SPARK-28012][SQL] Hive UDF supports struct type foldable expression 2019-06-20 14:36:01 +09:00
hive-thriftserver [SPARK-28104][SQL] Implement Spark's own GetColumnsOperation 2019-06-22 09:15:07 -07:00
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.