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https://issues.apache.org/jira/browse/IMPALA-889?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17902313#comment-17902313
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ASF subversion and git services commented on IMPALA-889:
--------------------------------------------------------
Commit 81f2673883f65aa71f682bf9fda6dd73888e75a8 in impala's branch
refs/heads/master from Mihaly Szjatinya
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=81f267388 ]
IMPALA-889: Add trim() function matching ANSI SQL definition
As agreed in JIRA discussions, the current PR extends existing TRIM
functionality with the support of SQL-standardized TRIM-FROM syntax:
TRIM({[LEADING / TRAILING / BOTH] | [STRING characters]} FROM expr).
Implemented based on the existing LTRIM / RTRIM / BTRIM family of
functions prepared earlier in IMPALA-6059 and extended for UTF-8 in
IMPALA-12718. Besides, partly based on abandoned PR
https://gerrit.cloudera.org/#/c/4474 and similar EXTRACT-FROM
functionality from https://github.com/apache/impala/commit/543fa73f3a846
f0e4527514c993cb0985912b06c.
Supported syntaxes:
Syntax #1 TRIM(<where> FROM <string>);
Syntax #2 TRIM(<charset> FROM <string>);
Syntax #3 TRIM(<where> <charset> FROM <string>);
"where": Case-insensitive trim direction. Valid options are "leading",
"trailing", and "both". "leading" means trimming characters from the
start; "trailing" means trimming characters from the end; "both" means
trimming characters from both sides. For Syntax #2, since no "where"
is specified, the option "both" is implied by default.
"charset": Case-sensitive characters to be removed. This argument is
regarded as a character set going to be removed. The occurrence order
of each character doesn't matter and duplicated instances of the same
character will be ignored. NULL argument implies " " (standard space)
by default. Empty argument ("" or '') makes TRIM return the string
untouched. For Syntax #1, since no "charset" is specified, it trims
" " (standard space) by default.
"string": Case-sensitive target string to trim. This argument can be
NULL.
The UTF8_MODE query option is honored by TRIM-FROM, similarly to
existing TRIM().
UTF8_TRIM-FROM can be used to force UTF8 mode regardless of the query
option.
Design Notes:
1. No-BE. Since the existing LTRIM / RTRIM / BTRIM functions fully cover
all needed use-cases, no backend logic is required. This differs from
similar EXTRACT-FROM.
2. Syntax wrapper. TrimFromExpr class was introduced as a syntax
wrapper around FunctionCallExpr, which instantiates one of the regular
LTRIM / RTRIM / BTRIM functions. TrimFromExpr's role is to maintain
the integrity of the "phantom" TRIM-FROM built-in function.
3. No TRIM keyword. Following EXTRACT-FROM, no "TRIM" keyword was
added to the language. Although generally a keyword would allow easier
and better parsing, on the negative side it restricts token's usage in
general context. However, leading/trailing/both, being previously
saved as reserved words, are now added as keywords to make possible
their usage with no escaping.
Change-Id: I3c4fa6d0d8d0684c4b6d8dac8fd531d205e4f7b4
Reviewed-on: http://gerrit.cloudera.org:8080/21825
Reviewed-by: Csaba Ringhofer <[email protected]>
Tested-by: Csaba Ringhofer <[email protected]>
> Add trim() function matching ANSI SQL definition
> ------------------------------------------------
>
> Key: IMPALA-889
> URL: https://issues.apache.org/jira/browse/IMPALA-889
> Project: IMPALA
> Issue Type: New Feature
> Components: Backend
> Affects Versions: Impala 1.2.4
> Reporter: Jonathan Seidman
> Assignee: Mihaly Szjatinya
> Priority: Minor
> Labels: ansi-sql, built-in-function, ramp-up
>
> Add support for an ISO-SQL compliant trim() function, i.e. trim([leading |
> trailing | both] [characters] from string). Lack of this impacts users of BI
> tools migrating existing SQL from other systems.
> Reference:
> https://my.vertica.com/docs/8.1.x/HTML/index.htm#Authoring/SQLReferenceManual/Functions/String/TRIM.htm
> Part of the ANSI definition
> {noformat}
> <trim function> ::=
> TRIM <left paren> <trim operands> <right paren>
> <trim operands> ::=
> [ [ <trim specification> ] [ <trim character> ] FROM ] <trim source>
> <trim source> ::=
> <character value expression>
> <trim specification> ::=
> LEADING
> | TRAILING
> | BOTH
> {noformat}
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