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Posted to issues-all@impala.apache.org by "Alex Rodoni (Jira)" <ji...@apache.org> on 2019/09/14 01:47:00 UTC
[jira] [Updated] (IMPALA-8945) Impala Doc: Incorrect Claim of
Equivalence in Impala Docs
[ https://issues.apache.org/jira/browse/IMPALA-8945?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Alex Rodoni updated IMPALA-8945:
--------------------------------
Description:
The Impala docs entry for the IS DISTINCT FROM operator states:
The <=> operator, used like an equality operator in a join query, is more efficient than the equivalent clause: A = B OR (A IS NULL AND B IS NULL). The <=> operator can use a hash join, while the OR expression cannot.
But this expression is not equivalent to A <=> B. See the attached screenshot demonstrating their non-equivalence. An expression that is equivalent to A <=> B is this:
(A IS NULL AND B IS NULL) OR ((A IS NOT NULL AND B IS NOT NULL) AND (A = B))
This expression should replace the existing incorrect expression.
> Impala Doc: Incorrect Claim of Equivalence in Impala Docs
> ---------------------------------------------------------
>
> Key: IMPALA-8945
> URL: https://issues.apache.org/jira/browse/IMPALA-8945
> Project: IMPALA
> Issue Type: Bug
> Components: Docs
> Reporter: Alex Rodoni
> Assignee: Alex Rodoni
> Priority: Major
>
> The Impala docs entry for the IS DISTINCT FROM operator states:
> The <=> operator, used like an equality operator in a join query, is more efficient than the equivalent clause: A = B OR (A IS NULL AND B IS NULL). The <=> operator can use a hash join, while the OR expression cannot.
> But this expression is not equivalent to A <=> B. See the attached screenshot demonstrating their non-equivalence. An expression that is equivalent to A <=> B is this:
> (A IS NULL AND B IS NULL) OR ((A IS NOT NULL AND B IS NOT NULL) AND (A = B))
> This expression should replace the existing incorrect expression.
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