[jira] [Created] (ASTERIXDB-2476) Support array slicing in SQL++

["Till (JIRA)" <ji...@apache.org>]

Till created ASTERIXDB-2476:
-------------------------------

             Summary: 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


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.



--
This message was sent by Atlassian JIRA
(v7.6.3#76005)