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https://issues.apache.org/jira/browse/PHOENIX-3390?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15958147#comment-15958147
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James Taylor commented on PHOENIX-3390:
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Thanks, [~talktoswa...@gmail.com]! Let's finish this off so we can commit it.
bq. we'd want to make sure that you can include any expression in the
arguments, for example, approx_sum(col1/col2 * col3)
When HLL sees it, the expression would have already been evaluated. It's just
general SQL syntax that we'd need to support - just make sure you have a test
for it - it likely already works. One common use of an expression inside of an
aggregate function would be to have a COALESCE call that causes a null value to
be treated differently, like this {{APPROX_SUM(COALESCE(col1, 0))}}
> Custom UDAF for HyperLogLogPlus
> -------------------------------
>
> Key: PHOENIX-3390
> URL: https://issues.apache.org/jira/browse/PHOENIX-3390
> Project: Phoenix
> Issue Type: New Feature
> Reporter: Swapna Kasula
> Priority: Minor
>
> With ref # PHOENIX-2069
> Custome UDAF to aggregate/union of Hyperloglog's of a column and returns a
> Hyperloglog.
> select hllUnion(col1) from table; //returns a Hyperloglog, which is the
> union of all hyperloglog's from all rows for column 'col1'
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