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https://issues.apache.org/jira/browse/CALCITE-4997?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17489885#comment-17489885
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xiong duan commented on CALCITE-4997:
-------------------------------------
The PR looks good to me. If have another contributor to review it, then we can
merge it.
> Keep APPROX_COUNT_DISTINCT in some SqlDialects
> ----------------------------------------------
>
> 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
> Labels: pull-request-available
> Time Spent: 40m
> Remaining Estimate: 0h
>
> Summary: Some engines support APPROX_COUNT_DISTINCT function, while others
> do not. So we can use the parameter *SqlDialect#supportsApproxCountDistinct*
> to control whether to use APPROX_COUNT_DISTINCT(It is APPROX_DISTINCT for
> Presto).
> ----
> Problem: Before fix for all SqlDialects
> {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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