Fixed relation data GC + PostgreSQL bug

https://github.com/craftcms/cms/issues/9905#issuecomment-1478490012

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Release Notes for Craft CMS 3.x
 
+## Unreleased
+
+- Fixed a bug where relation data was getting deleted when running garbage collection on PostgreSQL. ([#9905](https://github.com/craftcms/cms/issues/9905))
+
 ## 3.8.4 - 2023-03-20
 
 - The `|json_encode` Twig filter now calls `craft\helpers\Json::encode()` internally, improving error handling. ([#12919](https://github.com/craftcms/cms/issues/12919))

src/services/Gc.php

@@ -364,7 +364,9 @@ SQL;
 DELETE FROM $relationsTable
 USING $relationsTable [[r]]
 LEFT JOIN $elementsTable [[e]] ON [[e.id]] = [[r.targetId]]
-WHERE [[e.id]] IS NULL
+WHERE
+  $relationsTable.[[id]] = [[r.id]] AND
+  [[e.id]] IS NULL
 SQL;
         }
 
@@ -390,8 +392,10 @@ SQL;
 DELETE FROM $structureElementsTable
 USING $structureElementsTable [[se]]
 LEFT JOIN $elementsTable [[e]] ON [[e.id]] = [[se.elementId]]
-WHERE $structureElementsTable.[[id]] = [[se.id]] AND
-  [[se.elementId]] IS NOT NULL AND [[e.id]] IS NULL
+WHERE
+  $structureElementsTable.[[id]] = [[se.id]] AND
+  [[se.elementId]] IS NOT NULL AND
+  [[e.id]] IS NULL
 SQL;
         }