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https://issues.apache.org/jira/browse/ASTERIXDB-2951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17401800#comment-17401800
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Dmitry Lychagin commented on ASTERIXDB-2951:
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https://asterix-gerrit.ics.uci.edu/c/asterixdb/+/12884
> Support IS [NOT] DISTINCT FROM operator
> ---------------------------------------
>
> Key: ASTERIXDB-2951
> URL: https://issues.apache.org/jira/browse/ASTERIXDB-2951
> Project: Apache AsterixDB
> Issue Type: Bug
> Components: COMP - Compiler
> Affects Versions: 0.9.7
> Reporter: Dmitry Lychagin
> Assignee: Dmitry Lychagin
> Priority: Major
> Fix For: 0.9.8
>
>
> SQL supports IS NOT DISTINCT FROM operator which is a comparison operator
> that also returns TRUE if both values are NULL.
> See SQL:1999 feature T151, “DISTINCT predicate” and SQL:2003 feature T152,
> “DISTINCT predicate with negation”.
> We need to implement IS [NOT] DISTINCT FROM operator in SQL++ extending it to
> support MISSING values as follows.
> "x IS NOT DISTINCT FROM y" returns true
> 1. if x and y are not unknown and x = y,
> 2. if both x and y are null,
> 3. if both x and y are missing
> otherwise it returns false.
> "x IS DISTINCT FROM y" returns: NOT(x IS NOT DISTINCT FROM y)
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