[jira] [Commented] (FLINK-3141) Design of NULL values handling in operation

["Timo Walther (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-3141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15240990#comment-15240990 ] 

Timo Walther commented on FLINK-3141:
-------------------------------------

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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