From 57247ed6ca1a61d19f26912be3ab1e19528996f2 Mon Sep 17 00:00:00 2001
From: d-ph <dph03292@gmail.com>
Date: Mon, 22 Jul 2024 10:06:18 +0100
Subject: [PATCH] Make CountWalker use COUNT(*) when $distinct is explicitly
 set to false (#11552)

This change makes CountWalker use COUNT(*) instead of
COUNT(tbl.id), when the user declared that their query
does not need to use (SELECT) DISTINCT, which is
commonly the case when there are no JOINs in the query,
or when the JOINs are only *ToOne.

Research showed that COUNT(*) allows databases to use
index(-only) scans more eagerly from any of the
indexed columns, especially when the query is using
a WHERE-condition that filters on an indexed column.
---
 src/Tools/Pagination/CountWalker.php          | 36 ++++++++++---------
 .../ORM/Tools/Pagination/CountWalkerTest.php  | 14 ++++++++
 2 files changed, 34 insertions(+), 16 deletions(-)

diff --git a/src/Tools/Pagination/CountWalker.php b/src/Tools/Pagination/CountWalker.php
index d2129435558..f11b25d6821 100644
--- a/src/Tools/Pagination/CountWalker.php
+++ b/src/Tools/Pagination/CountWalker.php
@@ -37,27 +37,31 @@ public function walkSelectStatement(SelectStatement $selectStatement): void
             throw new RuntimeException('Cannot count query which selects two FROM components, cannot make distinction');
         }
 
-        $fromRoot            = reset($from);
-        $rootAlias           = $fromRoot->rangeVariableDeclaration->aliasIdentificationVariable;
-        $rootClass           = $this->getMetadataForDqlAlias($rootAlias);
-        $identifierFieldName = $rootClass->getSingleIdentifierFieldName();
+        $distinct = $this->_getQuery()->getHint(self::HINT_DISTINCT);
 
-        $pathType = PathExpression::TYPE_STATE_FIELD;
-        if (isset($rootClass->associationMappings[$identifierFieldName])) {
-            $pathType = PathExpression::TYPE_SINGLE_VALUED_ASSOCIATION;
-        }
+        $countPathExpressionOrLiteral = '*';
+        if ($distinct) {
+            $fromRoot            = reset($from);
+            $rootAlias           = $fromRoot->rangeVariableDeclaration->aliasIdentificationVariable;
+            $rootClass           = $this->getMetadataForDqlAlias($rootAlias);
+            $identifierFieldName = $rootClass->getSingleIdentifierFieldName();
+
+            $pathType = PathExpression::TYPE_STATE_FIELD;
+            if (isset($rootClass->associationMappings[$identifierFieldName])) {
+                $pathType = PathExpression::TYPE_SINGLE_VALUED_ASSOCIATION;
+            }
 
-        $pathExpression       = new PathExpression(
-            PathExpression::TYPE_STATE_FIELD | PathExpression::TYPE_SINGLE_VALUED_ASSOCIATION,
-            $rootAlias,
-            $identifierFieldName,
-        );
-        $pathExpression->type = $pathType;
+            $countPathExpressionOrLiteral       = new PathExpression(
+                PathExpression::TYPE_STATE_FIELD | PathExpression::TYPE_SINGLE_VALUED_ASSOCIATION,
+                $rootAlias,
+                $identifierFieldName,
+            );
+            $countPathExpressionOrLiteral->type = $pathType;
+        }
 
-        $distinct                                         = $this->_getQuery()->getHint(self::HINT_DISTINCT);
         $selectStatement->selectClause->selectExpressions = [
             new SelectExpression(
-                new AggregateExpression('count', $pathExpression, $distinct),
+                new AggregateExpression('count', $countPathExpressionOrLiteral, $distinct),
                 null,
             ),
         ];
diff --git a/tests/Tests/ORM/Tools/Pagination/CountWalkerTest.php b/tests/Tests/ORM/Tools/Pagination/CountWalkerTest.php
index 5af90e87949..6a223e67f50 100644
--- a/tests/Tests/ORM/Tools/Pagination/CountWalkerTest.php
+++ b/tests/Tests/ORM/Tools/Pagination/CountWalkerTest.php
@@ -27,6 +27,20 @@ public function testCountQuery(): void
         );
     }
 
+    public function testCountQueryWithoutDistinctUsesCountStar(): void
+    {
+        $query = $this->entityManager->createQuery(
+            'SELECT p, c, a FROM Doctrine\Tests\ORM\Tools\Pagination\BlogPost p JOIN p.category c JOIN p.author a',
+        );
+        $query->setHint(Query::HINT_CUSTOM_TREE_WALKERS, [CountWalker::class]);
+        $query->setHint(CountWalker::HINT_DISTINCT, false);
+
+        self::assertEquals(
+            'SELECT count(*) AS sclr_0 FROM BlogPost b0_ INNER JOIN Category c1_ ON b0_.category_id = c1_.id INNER JOIN Author a2_ ON b0_.author_id = a2_.id',
+            $query->getSQL(),
+        );
+    }
+
     public function testCountQueryMixedResultsWithName(): void
     {
         $query = $this->entityManager->createQuery(