[jira] [Commented] (FLINK-18164) null <> 'str' should be true

["Benchao Li (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-18164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17151243#comment-17151243 ] 

Benchao Li commented on FLINK-18164:
------------------------------------

[~Leonard Xu] I've updated the issue description.

> null <> 'str' should be true
> ----------------------------
>
>                 Key: FLINK-18164
>                 URL: https://issues.apache.org/jira/browse/FLINK-18164
>             Project: Flink
>          Issue Type: Bug
>          Components: Table SQL / API
>            Reporter: Benchao Li
>            Priority: Major
>
> In ISO SQL standard, boolean is three-value type, including {{true}}, {{false}}, {{unknown.}}
> And in Flink SQL, we also go with the SQL standard, and the {{unknown}} will be {{null}}. For example:
>  
> {code:SQL}
> SELECT null <> null  -- null
> SELECT null <> 'hello'  -- null
> SELECT null = null  -- null
> SELECT null <> 'hello'  -- null
> {code}
>  
> In {{where}} clause, we evaluate `null` boolean to `false` by default. For example:
> {code:SQL}
> ... WHERE null <> null  -- evaluate to false, there is no output
> ... null <> 'hello'  -- evaluate to false, there is no output
> SELECT IF(null = null, 0, 1)  -- 1
> SELECT IF(null <> 'hello', 0, 1) -- 1
> {code}
> To make {{null}} comparable to others, use can use {{IS [NOT] DISTINCT FROM}}. For example:
> {code:SQL}
> SELECT null IS NOT DISTINCT FROM null  -- true
> SELECT null IS DISTINCT FROM 'hello'  -- true
> {code}
>  
> ~~~~~~~~original description~~~~~~~~
> Currently, if we compare null with other literals, the result will always be false.
>  It's because the code gen always gives a default value (false) for the result. And I think it's a bug if `null <> 'str'` is false.
> It's reported from user-zh: [http://apache-flink.147419.n8.nabble.com/flink-sql-null-false-td3640.html]
>  CC [~jark] [~ykt836]



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