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https://issues.apache.org/jira/browse/PHOENIX-3773?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16034333#comment-16034333
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Loknath Priyatham Teja Singamsetty commented on PHOENIX-3773:
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[~jamestaylor]
bq. Then, once you have all the values, combine them together using the
PArrayDataType.appendItemToArray() method
I tried this last week as well but for some reason the output is not as
expected. Yesterday made changes to use PArrayDataType.appendItemToArray(),
upon debugging found two things:
a) For fixed length data types, the appendItemToArray is actually prepending
the arrayBytes reversing the array construction. For the time being used
prependItemToArray() method instead which fixed this issue. The following lines
of code in appendItemToArray seems to be the reason behind this which copies
the new bytes to front of array and older bytes to the end.
{quote}
newArray = new byte[length + elementLength];
System.arraycopy(arrayBytes, offset, newArray, 0, length);
System.arraycopy(elementBytes, elementOffset, newArray, length,
elementLength);
{quote}
b) For variable length data types, the Array construction results in
ArrayIndexOutOfBoundsException. Here is the stack trace
java.lang.ArrayIndexOutOfBoundsException: 32767
at
org.apache.phoenix.schema.types.PArrayDataType.prependItemToArray(PArrayDataType.java:545)
at
org.apache.phoenix.expression.aggregator.FirstLastValueBaseClientAggregator.evaluate(FirstLastValueBaseClientAggregator.java:117)
at
org.apache.phoenix.schema.KeyValueSchema.toBytes(KeyValueSchema.java:112)
at
org.apache.phoenix.schema.KeyValueSchema.toBytes(KeyValueSchema.java:93)
at
org.apache.phoenix.expression.aggregator.Aggregators.toBytes(Aggregators.java:112)
at
org.apache.phoenix.iterate.BaseGroupedAggregatingResultIterator.next(BaseGroupedAggregatingResultIterator.java:82)
at
org.apache.phoenix.jdbc.PhoenixResultSet.next(PhoenixResultSet.java:778)
at
org.apache.phoenix.end2end.FirstValuesFunctionIT.varcharDatatypeSimpleTest(FirstValuesFunctionIT.java:100)
I'm debugging this further.
bq.Probably a good idea to have a test that asks for the top 3 values when
there are only 2 values to make sure that case works too (if you don't have
that already).
Test case is included already.
> Implement FIRST_VALUES aggregate function
> -----------------------------------------
>
> Key: PHOENIX-3773
> URL: https://issues.apache.org/jira/browse/PHOENIX-3773
> Project: Phoenix
> Issue Type: New Feature
> Reporter: James Taylor
> Assignee: Loknath Priyatham Teja Singamsetty
> Labels: SFDC
> Fix For: 4.11.0
>
> Attachments: PHOENIX-3773_4.x-HBase-0.98.patch,
> PHOENIX-3773_master.patch, PHOENIX-3773.patch, PHOENIX-3773.v2.patch,
> PHOENIX-3773.v3.patch
>
>
> Similar to FIRST_VALUE, but would allow the user to specify how many values
> to keep. This could use a MinMaxPriorityQueue under the covers and be much
> more efficient than using multiple NTH_VALUE calls to do the same like this:
> {code}
> SELECT entity_id,
> NTH_VALUE(user_id,1) WITHIN GROUP (ORDER BY last_read_date DESC) as
> nth1_user_id,
> NTH_VALUE(user_id,2) WITHIN GROUP (ORDER BY last_read_date DESC) as
> nth2_user_id,
> NTH_VALUE(user_id,3) WITHIN GROUP (ORDER BY last_read_date DESC) as
> nth3_user_id,
> count(*)
> FROM MY_TABLE
> WHERE tenant_id='00Dx0000000XXXX'
> AND entity_id in ('0D5x000000ABCD','0D5x000000ABCE')
> GROUP BY entity_id;
> {code}
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