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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-66812] Incorrect $group/$project optimization analysis can cause incorrect results for strange queries</title>
                <link>https://jira.mongodb.org/browse/SERVER-66812</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;We have some logic to detect when a projection underneath a $group stage is not needed and optimize it away. This analysis has some code that appears to be trying to check for a case like this and avoid removing the projection since it would impact the query results:&lt;/p&gt;
&lt;p/&gt;
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&lt;p/&gt;

&lt;p&gt;Unfortunately it looks like that analysis was implemented incorrectly and instead of checking if the projection provides all the fields that the $group needs, it appears to be checking something different. I think it&apos;s whether &lt;em&gt;none&lt;/em&gt; of the projection fields are needed by the $group? In any case, there is a demonstrable bug around this optimization that should be fixed. I&apos;ll attach a patch to demonstrate.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2056163">SERVER-66812</key>
            <summary>Incorrect $group/$project optimization analysis can cause incorrect results for strange queries</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="6" iconUrl="https://jira.mongodb.org/images/icons/statuses/closed.png" description="The issue is considered finished, the resolution is correct. Issues which are closed can be reopened.">Closed</status>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="13201">Fixed</resolution>
                                        <assignee username="charlie.swanson@mongodb.com">Charlie Swanson</assignee>
                                    <reporter username="charlie.swanson@mongodb.com">Charlie Swanson</reporter>
                        <labels>
                    </labels>
                <created>Thu, 26 May 2022 18:19:42 +0000</created>
                <updated>Sun, 29 Oct 2023 21:37:40 +0000</updated>
                            <resolved>Tue, 7 Jun 2022 17:55:12 +0000</resolved>
                                    <version>5.3.0</version>
                    <version>5.2.0</version>
                                    <fixVersion>6.0.0-rc9</fixVersion>
                    <fixVersion>6.1.0-rc0</fixVersion>
                                                        <votes>0</votes>
                                    <watches>10</watches>
                                                                                                                <comments>
                            <comment id="4602002" author="xgen-internal-githook" created="Wed, 8 Jun 2022 13:45:12 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Charlie Swanson&apos;, &apos;email&apos;: &apos;charlie.swanson@mongodb.com&apos;, &apos;username&apos;: &apos;cswanson310&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-66812&quot; title=&quot;Incorrect $group/$project optimization analysis can cause incorrect results for strange queries&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-66812&quot;&gt;&lt;del&gt;SERVER-66812&lt;/del&gt;&lt;/a&gt; Fix bug with $group projection analysis&lt;/p&gt;

&lt;p&gt;(cherry picked from commit 8a3af130c7dba9936b30e17d25dd52a5802658ad)&lt;br/&gt;
Branch: v6.0&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/904122d4b13bdc8382b36081afa47017ba7855dc&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/904122d4b13bdc8382b36081afa47017ba7855dc&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4598313" author="xgen-internal-githook" created="Mon, 6 Jun 2022 23:15:32 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Charlie Swanson&apos;, &apos;email&apos;: &apos;charlie.swanson@mongodb.com&apos;, &apos;username&apos;: &apos;cswanson310&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-66812&quot; title=&quot;Incorrect $group/$project optimization analysis can cause incorrect results for strange queries&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-66812&quot;&gt;&lt;del&gt;SERVER-66812&lt;/del&gt;&lt;/a&gt; Fix bug with $group projection analysis&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/8a3af130c7dba9936b30e17d25dd52a5802658ad&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/8a3af130c7dba9936b30e17d25dd52a5802658ad&lt;/a&gt;&lt;/p&gt;</comment>
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