diff --git a/lib/Doctrine/ORM/Tools/SchemaTool.php b/lib/Doctrine/ORM/Tools/SchemaTool.php
index 2e02279cc0c..89c878dbd69 100644
--- a/lib/Doctrine/ORM/Tools/SchemaTool.php
+++ b/lib/Doctrine/ORM/Tools/SchemaTool.php
@@ -578,6 +578,7 @@ private function gatherRelationsSql(
                 $this->gatherRelationJoinColumns(
                     $mapping['joinColumns'],
                     $table,
+                    $class,
                     $foreignClass,
                     $mapping,
                     $primaryKeyColumns,
@@ -608,6 +609,7 @@ private function gatherRelationsSql(
                     $joinTable['joinColumns'],
                     $theJoinTable,
                     $class,
+                    $class,
                     $mapping,
                     $primaryKeyColumns,
                     $addedFks,
@@ -618,6 +620,7 @@ private function gatherRelationsSql(
                 $this->gatherRelationJoinColumns(
                     $joinTable['inverseJoinColumns'],
                     $theJoinTable,
+                    $class,
                     $foreignClass,
                     $mapping,
                     $primaryKeyColumns,
@@ -685,6 +688,7 @@ private function gatherRelationJoinColumns(
         array $joinColumns,
         Table $theJoinTable,
         ClassMetadata $class,
+        ClassMetadata $foreignClass,
         array $mapping,
         array &$primaryKeyColumns,
         array &$addedFks,
@@ -693,12 +697,12 @@ private function gatherRelationJoinColumns(
         $localColumns      = [];
         $foreignColumns    = [];
         $fkOptions         = [];
-        $foreignTableName  = $this->quoteStrategy->getTableName($class, $this->platform);
+        $foreignTableName  = $this->quoteStrategy->getTableName($foreignClass, $this->platform);
         $uniqueConstraints = [];
 
         foreach ($joinColumns as $joinColumn) {
             [$definingClass, $referencedFieldName] = $this->getDefiningClass(
-                $class,
+                $foreignClass,
                 $joinColumn['referencedColumnName']
             );
 
@@ -710,10 +714,10 @@ private function gatherRelationJoinColumns(
                 );
             }
 
-            $quotedColumnName    = $this->quoteStrategy->getJoinColumnName($joinColumn, $class, $this->platform);
+            $quotedColumnName    = $this->quoteStrategy->getJoinColumnName($joinColumn, $foreignClass, $this->platform);
             $quotedRefColumnName = $this->quoteStrategy->getReferencedJoinColumnName(
                 $joinColumn,
-                $class,
+                $foreignClass,
                 $this->platform
             );
 
@@ -736,7 +740,10 @@ private function gatherRelationJoinColumns(
                     $columnOptions['columnDefinition'] = $fieldMapping['columnDefinition'];
                 }
 
-                if (isset($joinColumn['nullable'])) {
+                if (
+                    isset($joinColumn['nullable'])
+                    && ! ($class->isInheritanceTypeSingleTable() && $class->parentClasses)
+                ) {
                     $columnOptions['notnull'] = ! $joinColumn['nullable'];
                 }
 
diff --git a/tests/Doctrine/Tests/Models/Company/CompanyCarContract.php b/tests/Doctrine/Tests/Models/Company/CompanyCarContract.php
new file mode 100644
index 00000000000..146eba03f3a
--- /dev/null
+++ b/tests/Doctrine/Tests/Models/Company/CompanyCarContract.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Doctrine\Tests\Models\Company;
+
+use Doctrine\ORM\Mapping as ORM;
+use Doctrine\ORM\Mapping\Entity;
+
+/** @Entity */
+class CompanyCarContract extends CompanyContract
+{
+    /**
+     * @ORM\ManyToOne(targetEntity="CompanyCar")
+     * @ORM\JoinColumn(nullable=false, onDelete="CASCADE")
+     *
+     * @var CompanyCar
+     */
+    private $companyCar;
+
+    public function calculatePrice(): int
+    {
+        return 0;
+    }
+
+    public function setCompanyCar(CompanyCar $companyCar): void
+    {
+        $this->companyCar = $companyCar;
+    }
+}
diff --git a/tests/Doctrine/Tests/Models/Company/CompanyContract.php b/tests/Doctrine/Tests/Models/Company/CompanyContract.php
index b1a601670c3..ba799f2ff74 100644
--- a/tests/Doctrine/Tests/Models/Company/CompanyContract.php
+++ b/tests/Doctrine/Tests/Models/Company/CompanyContract.php
@@ -38,7 +38,8 @@
  * @DiscriminatorMap({
  *     "fix"       = "CompanyFixContract",
  *     "flexible"  = "CompanyFlexContract",
- *     "flexultra" = "CompanyFlexUltraContract"
+ *     "flexultra" = "CompanyFlexUltraContract",
+ *     "car"       = "CompanyCarContract"
  * })
  * @NamedNativeQueries({
  *      @NamedNativeQuery(
@@ -85,7 +86,7 @@
 #[ORM\Table(name: 'company_contracts')]
 #[ORM\InheritanceType('SINGLE_TABLE')]
 #[ORM\DiscriminatorColumn(name: 'discr', type: 'string')]
-#[ORM\DiscriminatorMap(['fix' => 'CompanyFixContract', 'flexible' => 'CompanyFlexContract', 'flexultra' => 'CompanyFlexUltraContract'])]
+#[ORM\DiscriminatorMap(['fix' => 'CompanyFixContract', 'flexible' => 'CompanyFlexContract', 'flexultra' => 'CompanyFlexUltraContract', 'car' => 'CompanyCarContract'])]
 #[ORM\EntityListeners(['CompanyContractListener'])]
 abstract class CompanyContract
 {
diff --git a/tests/Doctrine/Tests/ORM/Functional/SingleTableInheritanceTest.php b/tests/Doctrine/Tests/ORM/Functional/SingleTableInheritanceTest.php
index 935b4dd6e43..6995afe6cb4 100644
--- a/tests/Doctrine/Tests/ORM/Functional/SingleTableInheritanceTest.php
+++ b/tests/Doctrine/Tests/ORM/Functional/SingleTableInheritanceTest.php
@@ -7,6 +7,8 @@
 use Doctrine\Common\Collections\Criteria;
 use Doctrine\ORM\Mapping\ClassMetadata;
 use Doctrine\ORM\Persisters\MatchingAssociationFieldRequiresObject;
+use Doctrine\Tests\Models\Company\CompanyCar;
+use Doctrine\Tests\Models\Company\CompanyCarContract;
 use Doctrine\Tests\Models\Company\CompanyContract;
 use Doctrine\Tests\Models\Company\CompanyEmployee;
 use Doctrine\Tests\Models\Company\CompanyFixContract;
@@ -419,4 +421,23 @@ public function testEagerLoadInheritanceHierarchy(): void
 
         self::assertFalse($this->isUninitializedObject($contract->getSalesPerson()));
     }
+
+    public function testChildCanHaveNonNullableRelation(): void
+    {
+        $companyCar  = new CompanyCar('BMW');
+        $fixContract = new CompanyFixContract();
+        $carContract = new CompanyCarContract();
+        $carContract->setCompanyCar($companyCar);
+
+        $this->_em->persist($fixContract);
+        $this->_em->persist($companyCar);
+        $this->_em->persist($carContract);
+        $this->_em->flush();
+        $this->_em->clear();
+
+        $repo         = $this->_em->getRepository(CompanyCarContract::class);
+        $carContracts = $repo->findAll();
+
+        self::assertCount(1, $carContracts);
+    }
 }
diff --git a/tests/Doctrine/Tests/ORM/Query/SelectSqlGenerationTest.php b/tests/Doctrine/Tests/ORM/Query/SelectSqlGenerationTest.php
index 540d870828f..bc9811585e1 100644
--- a/tests/Doctrine/Tests/ORM/Query/SelectSqlGenerationTest.php
+++ b/tests/Doctrine/Tests/ORM/Query/SelectSqlGenerationTest.php
@@ -209,7 +209,7 @@ public function testSupportsJoinOnMultipleComponentsWithJoinedInheritanceType():
 
         $this->assertSqlGeneration(
             'SELECT c FROM Doctrine\Tests\Models\Company\CompanyContract c JOIN c.salesPerson s LEFT JOIN Doctrine\Tests\Models\Company\CompanyEvent e WITH s.id = e.id',
-            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7 FROM company_contracts c0_ INNER JOIN company_employees c1_ ON c0_.salesPerson_id = c1_.id LEFT JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id LEFT JOIN (company_events c4_ LEFT JOIN company_auctions c5_ ON c4_.id = c5_.id LEFT JOIN company_raffles c6_ ON c4_.id = c6_.id) ON (c2_.id = c4_.id) WHERE c0_.discr IN ('fix', 'flexible', 'flexultra')"
+            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7, c0_.companyCar_id AS companyCar_id_8 FROM company_contracts c0_ INNER JOIN company_employees c1_ ON c0_.salesPerson_id = c1_.id LEFT JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id LEFT JOIN (company_events c4_ LEFT JOIN company_auctions c5_ ON c4_.id = c5_.id LEFT JOIN company_raffles c6_ ON c4_.id = c6_.id) ON (c2_.id = c4_.id) WHERE c0_.discr IN ('fix', 'flexible', 'flexultra', 'car')"
         );
     }
 
@@ -1474,7 +1474,7 @@ public function testInheritanceTypeSingleTableInRootClassWithDisabledForcePartia
     {
         $this->assertSqlGeneration(
             'SELECT c FROM Doctrine\Tests\Models\Company\CompanyContract c',
-            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7 FROM company_contracts c0_ WHERE c0_.discr IN ('fix', 'flexible', 'flexultra')",
+            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7, c0_.companyCar_id AS companyCar_id_8 FROM company_contracts c0_ WHERE c0_.discr IN ('fix', 'flexible', 'flexultra', 'car')",
             [ORMQuery::HINT_FORCE_PARTIAL_LOAD => false]
         );
     }
@@ -1484,7 +1484,7 @@ public function testInheritanceTypeSingleTableInRootClassWithEnabledForcePartial
     {
         $this->assertSqlGeneration(
             'SELECT c FROM Doctrine\Tests\Models\Company\CompanyContract c',
-            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6 FROM company_contracts c0_ WHERE c0_.discr IN ('fix', 'flexible', 'flexultra')",
+            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6 FROM company_contracts c0_ WHERE c0_.discr IN ('fix', 'flexible', 'flexultra', 'car')",
             [ORMQuery::HINT_FORCE_PARTIAL_LOAD => true]
         );
     }
@@ -2054,7 +2054,7 @@ public function testSingleTableInheritanceLeftJoinWithCondition(): void
         // Regression test for the bug
         $this->assertSqlGeneration(
             'SELECT c FROM Doctrine\Tests\Models\Company\CompanyEmployee e LEFT JOIN Doctrine\Tests\Models\Company\CompanyContract c WITH c.salesPerson = e.id',
-            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7 FROM company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id LEFT JOIN company_contracts c0_ ON (c0_.salesPerson_id = c2_.id) AND c0_.discr IN ('fix', 'flexible', 'flexultra')"
+            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7, c0_.companyCar_id AS companyCar_id_8 FROM company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id LEFT JOIN company_contracts c0_ ON (c0_.salesPerson_id = c2_.id) AND c0_.discr IN ('fix', 'flexible', 'flexultra', 'car')"
         );
     }
 
@@ -2064,7 +2064,7 @@ public function testSingleTableInheritanceLeftJoinWithConditionAndWhere(): void
         // Ensure other WHERE predicates are passed through to the main WHERE clause
         $this->assertSqlGeneration(
             'SELECT c FROM Doctrine\Tests\Models\Company\CompanyEmployee e LEFT JOIN Doctrine\Tests\Models\Company\CompanyContract c WITH c.salesPerson = e.id WHERE e.salary > 1000',
-            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7 FROM company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id LEFT JOIN company_contracts c0_ ON (c0_.salesPerson_id = c2_.id) AND c0_.discr IN ('fix', 'flexible', 'flexultra') WHERE c1_.salary > 1000"
+            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7, c0_.companyCar_id AS companyCar_id_8 FROM company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id LEFT JOIN company_contracts c0_ ON (c0_.salesPerson_id = c2_.id) AND c0_.discr IN ('fix', 'flexible', 'flexultra', 'car') WHERE c1_.salary > 1000"
         );
     }
 
@@ -2074,7 +2074,7 @@ public function testSingleTableInheritanceInnerJoinWithCondition(): void
         // Test inner joins too
         $this->assertSqlGeneration(
             'SELECT c FROM Doctrine\Tests\Models\Company\CompanyEmployee e INNER JOIN Doctrine\Tests\Models\Company\CompanyContract c WITH c.salesPerson = e.id',
-            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7 FROM company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id INNER JOIN company_contracts c0_ ON (c0_.salesPerson_id = c2_.id) AND c0_.discr IN ('fix', 'flexible', 'flexultra')"
+            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7, c0_.companyCar_id AS companyCar_id_8 FROM company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id INNER JOIN company_contracts c0_ ON (c0_.salesPerson_id = c2_.id) AND c0_.discr IN ('fix', 'flexible', 'flexultra', 'car')"
         );
     }
 
@@ -2085,7 +2085,7 @@ public function testSingleTableInheritanceLeftJoinNonAssociationWithConditionAnd
         // the where clause when not joining onto that table
         $this->assertSqlGeneration(
             'SELECT c FROM Doctrine\Tests\Models\Company\CompanyContract c LEFT JOIN Doctrine\Tests\Models\Company\CompanyEmployee e WITH e.id = c.salesPerson WHERE c.completed = true',
-            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7 FROM company_contracts c0_ LEFT JOIN (company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id) ON (c2_.id = c0_.salesPerson_id) WHERE (c0_.completed = 1) AND c0_.discr IN ('fix', 'flexible', 'flexultra')"
+            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7, c0_.companyCar_id AS companyCar_id_8 FROM company_contracts c0_ LEFT JOIN (company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id) ON (c2_.id = c0_.salesPerson_id) WHERE (c0_.completed = 1) AND c0_.discr IN ('fix', 'flexible', 'flexultra', 'car')"
         );
     }
 
@@ -2097,7 +2097,7 @@ public function testSingleTableInheritanceJoinCreatesOnCondition(): void
         // via a join association
         $this->assertSqlGeneration(
             'SELECT c FROM Doctrine\Tests\Models\Company\CompanyContract c JOIN c.salesPerson s WHERE c.completed = true',
-            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7 FROM company_contracts c0_ INNER JOIN company_employees c1_ ON c0_.salesPerson_id = c1_.id LEFT JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id WHERE (c0_.completed = 1) AND c0_.discr IN ('fix', 'flexible', 'flexultra')"
+            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6, c0_.salesPerson_id AS salesPerson_id_7, c0_.companyCar_id AS companyCar_id_8 FROM company_contracts c0_ INNER JOIN company_employees c1_ ON c0_.salesPerson_id = c1_.id LEFT JOIN company_persons c2_ ON c1_.id = c2_.id LEFT JOIN company_managers c3_ ON c1_.id = c3_.id WHERE (c0_.completed = 1) AND c0_.discr IN ('fix', 'flexible', 'flexultra', 'car')"
         );
     }
 
@@ -2109,7 +2109,7 @@ public function testSingleTableInheritanceCreatesOnConditionAndWhere(): void
         // into the ON clause of the join
         $this->assertSqlGeneration(
             'SELECT e, COUNT(c) FROM Doctrine\Tests\Models\Company\CompanyEmployee e JOIN e.contracts c WHERE e.department = :department',
-            "SELECT c0_.id AS id_0, c0_.name AS name_1, c1_.salary AS salary_2, c1_.department AS department_3, c1_.startDate AS startDate_4, c2_.title AS title_5, COUNT(c3_.id) AS sclr_6, c0_.discr AS discr_7, c0_.spouse_id AS spouse_id_8, c2_.car_id AS car_id_9 FROM company_employees c1_ INNER JOIN company_persons c0_ ON c1_.id = c0_.id LEFT JOIN company_managers c2_ ON c1_.id = c2_.id INNER JOIN company_contract_employees c4_ ON c1_.id = c4_.employee_id INNER JOIN company_contracts c3_ ON c3_.id = c4_.contract_id AND c3_.discr IN ('fix', 'flexible', 'flexultra') WHERE c1_.department = ?",
+            "SELECT c0_.id AS id_0, c0_.name AS name_1, c1_.salary AS salary_2, c1_.department AS department_3, c1_.startDate AS startDate_4, c2_.title AS title_5, COUNT(c3_.id) AS sclr_6, c0_.discr AS discr_7, c0_.spouse_id AS spouse_id_8, c2_.car_id AS car_id_9 FROM company_employees c1_ INNER JOIN company_persons c0_ ON c1_.id = c0_.id LEFT JOIN company_managers c2_ ON c1_.id = c2_.id INNER JOIN company_contract_employees c4_ ON c1_.id = c4_.employee_id INNER JOIN company_contracts c3_ ON c3_.id = c4_.contract_id AND c3_.discr IN ('fix', 'flexible', 'flexultra', 'car') WHERE c1_.department = ?",
             [],
             ['department' => 'foobar']
         );