[
https://issues.apache.org/jira/browse/CALCITE-2035?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16242550#comment-16242550
]
Julian Hyde commented on CALCITE-2035:
--------------------------------------
It is done the same way as before. If you do count-distinct in Drill and you
don't allow approximate, your query won't plan.
I wrote the specification to give us freedom in future. I didn't change the
implementation.
> Add APPROX_COUNT_DISTINCT aggregate function
> --------------------------------------------
>
> Key: CALCITE-2035
> URL: https://issues.apache.org/jira/browse/CALCITE-2035
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
>
> Add {{APPROX_COUNT_DISTINCT}} aggregate function. The effect of
> {{APPROX_COUNT_DISTINCT(args)}} is the same as {{COUNT(DISTINCT args)}} but
> the planner may generate approximate results (e.g. by using HyperLogLog).
> Note "may" not "must", above: the planner may choose a plan that returns
> exact results.
> This is a step towards CALCITE-1588, which would allow an {{APPROXIMATE}}
> clause and specify in more detail the degree of approximation allowed.
--
This message was sent by Atlassian JIRA
(v6.4.14#64029)
