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<td class="page-title-pattern-first-line " style="padding: 0; border-collapse: collapse; font-family: Arial, sans-serif; font-size: 14px; padding-top: 10px"> <a href="https://hibernate.atlassian.net/browse/HHH" style="color: #3b73af; text-decoration: none">Hibernate ORM</a> / <a href="https://hibernate.atlassian.net/browse/HHH-11538" style="color: #3b73af; text-decoration: none"><img src="cid:jira-generated-image-avatar-d06ca5e8-8cfa-4f65-ae98-e22c7d892f63" height="16" width="16" border="0" align="absmiddle" alt="Bug" style="vertical-align: text-bottom"></a> <a href="https://hibernate.atlassian.net/browse/HHH-11538" style="color: #3b73af; text-decoration: none">HHH-11538</a> </td>
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<td style="vertical-align: top;; padding: 0; border-collapse: collapse; padding-right: 5px; font-size: 20px; line-height: 30px; mso-line-height-rule: exactly" class="page-title-pattern-header-container"> <span class="page-title-pattern-header" style="font-family: Arial, sans-serif; padding: 0; font-size: 20px; line-height: 30px; mso-text-raise: 2px; mso-line-height-rule: exactly; vertical-align: middle"> <a href="https://hibernate.atlassian.net/browse/HHH-11538" style="color: #3b73af; text-decoration: none">Redundant left outer joins in generated SQL</a> </span> </td>
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<td class="has-icon" style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <img src="cid:jira-generated-image-avatar-d06ca5e8-8cfa-4f65-ae98-e22c7d892f63" height="16" width="16" border="0" align="absmiddle" alt="Bug" style="vertical-align: text-bottom"> Bug </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Affects Versions:</th>
<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> 5.1.4, 5.2.8 </td>
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<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> Unassigned </td>
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<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> hibernate-core, query-hql </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Created:</th>
<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> 02/Mar/2017 00:03 AM </td>
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<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> joins query sqlquery </td>
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<td class="has-icon" style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <img src="cid:jira-generated-image-static-major-46b1dd6e-efbc-451a-9070-2ad6acb1087d" height="16" width="16" border="0" align="absmiddle" alt="Major" style="vertical-align: text-bottom"> Major </td>
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<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <a class="user-hover" rel="stasal" id="email_stasal" href="https://hibernate.atlassian.net/secure/ViewProfile.jspa?name=stasal" style="color:#6c797f;; color: #3b73af; text-decoration: none">Stanislav Alekminskiy</a> </td>
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<td class="text-paragraph-pattern-container mobile-resize-text " style="padding: 0; border-collapse: collapse; padding: 0 0 10px"> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0; margin-top: 0">Redundant left outer joins generated in SQL query when HQL query contains left join on some entity (not by primary key).</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">HQL: select c.inventoryNumber from Employee e left join Computer c on c.workplace = e.workplace</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">Generated SQL: </p>
<div class="preformatted panel" style="border-width: 1px;; border: 1px solid #cccccc; background: #f5f5f5; font-size: 12px; line-height: 1.333; font-family: monospace; border: 1px solid #cccccc; -moz-border-radius: 3px; border-radius: 3px; margin: 9px 0">
<div class="preformattedContent panelContent" style="padding: 9px 12px">
<pre style="margin: 10px 0 0; margin-top: 0; max-height: 30em; overflow: auto; white-space: pre-wrap; word-wrap: normal; white-space: pre; word-break: normal; word-wrap: break-word; word-break: break-all; white-space: pre-wrap">select
computer1_.Inventory_Number as col_0_0_
from
Employees employee0_
left outer join
Workplaces workplace3_
on employee0_.Workplace_ID=workplace3_.Workplace_ID
left outer join
Computers computer1_
on (
computer1_.Workplace_ID=employee0_.Workplace_ID
)
left outer join
Workplaces workplace2_
on computer1_.Workplace_ID=workplace2_.Workplace_ID
</pre>
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</div> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">And if there is join by primary key: select c.inventoryNumber from Employee e left join Computer c on c.workplace*.id* = e.workplace*.id*</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">Then the generated SQL looks like:</p>
<div class="preformatted panel" style="border-width: 1px;; border: 1px solid #cccccc; background: #f5f5f5; font-size: 12px; line-height: 1.333; font-family: monospace; border: 1px solid #cccccc; -moz-border-radius: 3px; border-radius: 3px; margin: 9px 0">
<div class="preformattedContent panelContent" style="padding: 9px 12px">
<pre style="margin: 10px 0 0; margin-top: 0; max-height: 30em; overflow: auto; white-space: pre-wrap; word-wrap: normal; white-space: pre; word-break: normal; word-wrap: break-word; word-break: break-all; white-space: pre-wrap">select
computer1_.Inventory_Number as col_0_0_
from
Employees employee0_
left outer join
Computers computer1_
on (
computer1_.Workplace_ID=employee0_.Workplace_ID
)
</pre>
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</div> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">No redundant joins here.</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">The problem is that such SQL significantly impacts performance when selecting from several large tables.</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">To reproduce you can run the following test and see the generated query in output: org.hibernate.bugs.QueryGenerationTestCase#testRedundantSqlJoins<br> from <a href="https://github.com/stasal/hibernate-tests" class="external-link" rel="nofollow" style="color: #3b73af; text-decoration: none">https://github.com/stasal/hibernate-tests</a></p> </td>
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