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https://issues.apache.org/jira/browse/PHOENIX-10?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13890932#comment-13890932
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James Taylor commented on PHOENIX-10:
-------------------------------------
The array column will have been projected into the scan, so you'll have the
KeyValue that with the entire array as its byte value in the List<KeyValue>
result. You'd need to use the logic for accessing a particular array element.
You could access a particular element by doing the following:
/**
* Serialized over from the client a List<ArrayIndexExpression> of all the
array index expressions
* The ArrayIndexExpression will contain a KeyValueColumnExpression as a child.
* Use the KeyValueExpressionVisitor to form a parallel array of
List<KeyValueColumnExpression>
* You can use this List to detect which KeyValues in the result should be
extracted and placed
* in your single, specially named KeyValue. Once detected, evaluate the
corresponding
* ArrayIndexExpression like this:
*/
Tuple tuple = new MultiKeyValueTuple(keyValues);
ArrayIndexExpression elemExpr = elemExprList.get(i);
elemExpr.evaluate(tuple, ptr);
// At this point, ptr will be pointing at the array element, so you'd want to
add
// it to your byte array your building that will hold all the referenced array
elements
I think this kind of post-processing is best done in a coprocessor, as you can
allocate your byte array that'll hold all the referenced array elements and
just add to it all in the scope of a single function.
> Push projection of a single ARRAY element to the server
> -------------------------------------------------------
>
> Key: PHOENIX-10
> URL: https://issues.apache.org/jira/browse/PHOENIX-10
> Project: Phoenix
> Issue Type: Improvement
> Reporter: James Taylor
> Assignee: ramkrishna.s.vasudevan
>
> If only a single array element is selected, we'll still return the entire
> array back to the client. Instead, we should push this to the server and only
> return the single array element. The same goes for the reference to an ARRAY
> in the WHERE clause. There's a general HBase fix for this (i.e. the ability
> to define a separate set of key values that will be returned versus key
> values available to filters) that has a patch here, but is deemed not
> possible to pull into the 0.94 branch by @lhofhansl.
> My thought is that we can add a Filter at the end our our filter chain that
> filters out any KeyValues that aren't in the SELECT expressions (i.e. filter
> out if a column is referenced in the WHERE clause, but not in the SELECT
> expressions). This same Filter could handle returning only the elements of
> the array that are referenced in the SELECT expression rather than the entire
> array.
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