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https://issues.apache.org/jira/browse/SPARK-47409?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uroš Bojanić updated SPARK-47409:
---------------------------------
    Summary: StringTrim & StringTrimLeft/Right/Both (binary & lowercase 
collation only)  (was: StringTrim & StringTrimLeft/Right/Both (all collations))

> StringTrim & StringTrimLeft/Right/Both (binary & lowercase collation only)
> --------------------------------------------------------------------------
>
>                 Key: SPARK-47409
>                 URL: https://issues.apache.org/jira/browse/SPARK-47409
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL
>    Affects Versions: 4.0.0
>            Reporter: Uroš Bojanić
>            Priority: Major
>              Labels: pull-request-available
>
> Enable collation support for the *StringTrim* built-in string function in 
> Spark (including {*}StringTrimBoth{*}, {*}StringTrimLeft{*}, 
> {*}StringTrimRight{*}). First confirm what is the expected behaviour for 
> these functions when given collated strings, and then move on to 
> implementation and testing. One way to go about this is to consider using 
> {_}StringSearch{_}, an efficient ICU service for string matching. Implement 
> the corresponding unit tests (CollationStringExpressionsSuite) and E2E tests 
> (CollationSuite) to reflect how this function should be used with collation 
> in SparkSQL, and feel free to use your chosen Spark SQL Editor to experiment 
> with the existing functions to learn more about how they work. In addition, 
> look into the possible use-cases and implementation of similar functions 
> within other other open-source DBMS, such as 
> [PostgreSQL|[https://www.postgresql.org/docs/]].
>  
> The goal for this Jira ticket is to implement the *StringTrim* function so it 
> supports all collation types currently supported in Spark. To understand what 
> changes were introduced in order to enable full collation support for other 
> existing functions in Spark, take a look at the Spark PRs and Jira tickets 
> for completed tasks in this parent (for example: Contains, StartsWith, 
> EndsWith).
>  
> Read more about ICU [Collation Concepts|http://example.com/] and 
> [Collator|http://example.com/] class, as well as _StringSearch_ using the 
> [ICU user 
> guide|https://unicode-org.github.io/icu/userguide/collation/string-search.html]
>  and [ICU 
> docs|https://unicode-org.github.io/icu-docs/apidoc/released/icu4j/com/ibm/icu/text/StringSearch.html].
>  Also, refer to the Unicode Technical Standard for string 
> [searching|https://www.unicode.org/reports/tr10/#Searching] and 
> [collation|https://www.unicode.org/reports/tr35/tr35-collation.html#Collation_Type_Fallback].



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