MDL-76155 qbank_comment: Move comment count queries to a JOIN

question/bank/comment/classes/comment_count_column.php

@@ -83,15 +83,7 @@ public function get_title(): string {
      * @param string $rowclasses Classes that can be added.
      */
     protected function display_content($question, $rowclasses): void {
-        global $DB;
         $syscontext = \context_system::instance();
-        $args = [
-            'component' => 'qbank_comment',
-            'commentarea' => 'question',
-            'itemid' => $question->id,
-            'contextid' => $syscontext->id,
-        ];
-        $commentcount = $DB->count_records('comments', $args);
         $attributes = [];
         if (question_has_capability_on($question, 'comment')) {
             $target = 'questioncommentpreview_' . $question->id;
@@ -103,7 +95,27 @@ protected function display_content($question, $rowclasses): void {
                 'data-contextid' => $syscontext->id,
             ];
         }
-        echo \html_writer::tag('a', $commentcount, $attributes);
+        echo \html_writer::tag('a', $question->commentcount ?? 0, $attributes);
+    }
+
+    public function get_extra_joins(): array {
+        $syscontext = \context_system::instance();
+        $subquery = "
+            SELECT COUNT('x') AS commentcount, itemid AS questionid
+            FROM {comments} c
+            WHERE c.component = 'qbank_comment'
+                  AND commentarea = 'question'
+                  AND contextid = {$syscontext->id}
+            GROUP BY c.itemid
+        ";
+
+        return [
+            'comments' => "LEFT JOIN ({$subquery}) comments ON comments.questionid = q.id"
+        ];
+    }
+
+    public function get_required_fields(): array {
+        return ['comments.commentcount AS commentcount'];
     }
 
     public function get_extra_classes(): array {