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https://issues.apache.org/jira/browse/IMPALA-8945?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alex Rodoni updated IMPALA-8945:
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Description:
Reported by [~icook]
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.
Another expression that is equivalent to A <=> B is:
if(A IS NULL OR B IS NULL, A IS NULL AND B IS NULL, A = B)
This one is a bit easier to follow. If you use this one in the docs, just
replace the following line with:
The <=> operator can use a hash join, while the if expression cannot.
was:
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.
Another expression that is equivalent to A <=> B is:
if(A IS NULL OR B IS NULL, A IS NULL AND B IS NULL, A = B)
This one is a bit easier to follow. If you use this one in the docs, just
replace the following line with:
The <=> operator can use a hash join, while the if expression cannot.
> 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
>
> Reported by [~icook]
> 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.
> Another expression that is equivalent to A <=> B is:
> if(A IS NULL OR B IS NULL, A IS NULL AND B IS NULL, A = B)
> This one is a bit easier to follow. If you use this one in the docs, just
> replace the following line with:
> The <=> operator can use a hash join, while the if expression cannot.
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