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https://issues.apache.org/jira/browse/ASTERIXDB-2476?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Murtadha Hubail reassigned ASTERIXDB-2476:
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Assignee: Hussain Towaileb
> Support array slicing in SQL++
> ------------------------------
>
> Key: ASTERIXDB-2476
> URL: https://issues.apache.org/jira/browse/ASTERIXDB-2476
> Project: Apache AsterixDB
> Issue Type: Improvement
> Components: COMP - Compiler, FUN - Functions
> Affects Versions: 0.9.5
> Reporter: Till
> Assignee: Hussain Towaileb
> Priority: Major
>
> Some programming languages support array slicing - the ability to extract sub
> arrays from array, which would be useful in SQL++. E.g. to retrieve the 2
> elements in the middle of {{["a","b","c","d"]}} one could write
> {{["a","b","c","d"][1:3]}} and get {{["b","c"]}}.
> To implement this, we should first add a function {{array_slice}} with 3
> parameters:
> # {{array}},
> # {{start}}, and
> # {{end}}.
> The function returns {{NULL}} if
> * {{array}} is not an array,
> * {{start}} is not a number _or_ greater than the length of the array, or
> * {{end}} is not a number _or_ greater than the length of the array _or_
> less than {{start}} _or_ {{MISSING}}.
> Otherwise {{array_slice(array, start, end)}} returns a subset of the source
> array, containing the elements from position {{start}} to {{end-1}}.
> The element at {{start}} is included, while the element at {{end}} is not.
> The array index starts with 0.
> If {{end}} is {{MISSING}}, all elements from start to the end of the source
> array are included.
> Negative positions are counted backwards from the end of the array.
> With that function we can extend the parser to support the slicing syntax
> {{array_expression [start_expression : [ end_expression ] ]}} and rewrite
> this syntax to a call of the function {{array_slice}} where a missing
> {{end_expression}} in the syntax is rewritten to passing a {{MISSING}}
> parameter as the 3rd argument.
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