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https://issues.apache.org/jira/browse/CALCITE-4997?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17486232#comment-17486232
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xiejiajun commented on CALCITE-4997:
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The result of `count distinct` is accurate, but it takes a lot of time to
calculate. When users use `approx_count_distinct`, they want to get an
approximate value quickly. If it becomes `count distinct`, users have to wait
for a long time.
> approx_count_distinct function was incorrectly converted to count(distinct )
> ----------------------------------------------------------------------------
>
> Key: CALCITE-4997
> URL: https://issues.apache.org/jira/browse/CALCITE-4997
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.29.0
> Reporter: xiejiajun
> Priority: Major
>
> {code:java}
> SELECT APPROX_COUNT_DISTINCT(product_id)
> FROM foodmart.product
> {code}
> will be
> {code:java}
> SELECT COUNT(DISTINCT product_id)
> FROM foodmart.product
> {code}
> This can cause many tasks to run too slowly.
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