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https://issues.apache.org/jira/browse/CALCITE-3881?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17069076#comment-17069076
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Julian Hyde commented on CALCITE-3881:
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Your fix only works for 0 <= months < 24. You should make it work for any
months value, including negative. Which probably means calling {{floorMod}}.
I think the fix should be in {{SqlFunctions.addMonths}} (Calcite), not
ymdToUnixDate (Avatica). ymdToUnixDate assumes that month is between 1 and 12,
and it should continue to do so. Its javadoc should state what it needs;
perhaps there should be an assert or throw IllegalArgumentException.
> SqlFunctions#addMonths yields incorrect results in some corner case
> -------------------------------------------------------------------
>
> Key: CALCITE-3881
> URL: https://issues.apache.org/jira/browse/CALCITE-3881
> Project: Calcite
> Issue Type: Bug
> Components: avatica
> Affects Versions: avatica-1.16.0
> Reporter: Zhenghua Gao
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> SqlFunctions#addMonths use DateTimeUtils#ymdToUnixDate to calculate the
> JDN(julian day number). But in some corner cases it yields incorrent results.
> The root cause is: the algorithm of DateTimeUtils#ymdToUnixDate requires
> reasonable month(1 to 12)[1], but SqlFunctions#addMonths may pass in a month
> out of the reasonable range.
> BTW: I didn't find the reference of the original paper of the algorithm, but
> an jdn explanation. Please correct me if anyone can find the original paper.
>
> The following case can reproduce the bug:
> addMonth('2019-09-01', 6) should yield '2020-03-01'
> {code:java}
> @Test public void testAddMonths() {
> checkAddMonths(2019, 9, 1, 2020, 3, 1, 6);
> } {code}
>
> [1]
> [http://www.cs.utsa.edu/~cs1063/projects/Spring2011/Project1/jdn-explanation.html]
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