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https://issues.apache.org/jira/browse/FLINK-3141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15240990#comment-15240990
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Timo Walther commented on FLINK-3141:
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I think we can close this issue, right?
> Design of NULL values handling in operation
> -------------------------------------------
>
> Key: FLINK-3141
> URL: https://issues.apache.org/jira/browse/FLINK-3141
> Project: Flink
> Issue Type: Sub-task
> Components: Table API
> Reporter: Chengxiang Li
>
> We discuss and finalize how NULL value is handled in specified cases here.
> this is the first proposal:
> # NULL compare. In ascending order, NULL is smaller than any other value, and
> NULL == NULL return false.
> # NULL exists in GroupBy Key, all NULL values are grouped as a single group.
> # NULL exists in Aggregate columns, ignore NULL in aggregation function.
> # NULL exists in both side Join key, refer to #i, NULL == NULL return false,
> no output for NULL Join key.
> # NULL in Scalar expression, expression within NULL(eg. 1 + NULL) return
> NULL.
> # NULL in Boolean expression, add an extra result: UNKNOWN, more semantic for
> Boolean expression in reference #1.
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