diff --git a/lib/dml/moodle_database.php b/lib/dml/moodle_database.php
index 021706be01a..c0b574ddf56 100644
--- a/lib/dml/moodle_database.php
+++ b/lib/dml/moodle_database.php
@@ -1954,6 +1954,29 @@ abstract class moodle_database {
         return $this->delete_records_select($table, $select, $params);
     }
 
+    /**
+     * Deletes records from a table using a subquery. The subquery should return a list of values
+     * in a single column, which match one field from the table being deleted.
+     *
+     * The $alias parameter must be set to the name of the single column in your subquery result
+     * (e.g. if the subquery is 'SELECT id FROM whatever', then it should be 'id'). This is not
+     * needed on most databases, but MySQL requires it.
+     *
+     * (On database where the subquery is inefficient, it is implemented differently.)
+     *
+     * @param string $table Table to delete from
+     * @param string $field Field in table to match
+     * @param string $alias Name of single column in subquery e.g. 'id'
+     * @param string $subquery Subquery that will return values of the field to delete
+     * @param array $params Parameters for subquery
+     * @throws dml_exception If there is any error
+     * @since Moodle 3.10
+     */
+    public function delete_records_subquery(string $table, string $field, string $alias,
+            string $subquery, array $params = []): void {
+        $this->delete_records_select($table, $field . ' IN (' . $subquery . ')', $params);
+    }
+
     /**
      * Delete one or more records from a table which match a particular WHERE clause.
      *
diff --git a/lib/dml/mysqli_native_moodle_database.php b/lib/dml/mysqli_native_moodle_database.php
index 8469c0d5003..69143936174 100644
--- a/lib/dml/mysqli_native_moodle_database.php
+++ b/lib/dml/mysqli_native_moodle_database.php
@@ -1662,6 +1662,23 @@ class mysqli_native_moodle_database extends moodle_database {
         return true;
     }
 
+    /**
+     * Deletes records using a subquery, which is done with a strange DELETE...JOIN syntax in MySQL
+     * because it performs very badly with normal subqueries.
+     *
+     * @param string $table Table to delete from
+     * @param string $field Field in table to match
+     * @param string $alias Name of single column in subquery e.g. 'id'
+     * @param string $subquery Query that will return values of the field to delete
+     * @param array $params Parameters for query
+     * @throws dml_exception If there is any error
+     */
+    public function delete_records_subquery(string $table, string $field, string $alias, string $subquery, array $params = []): void {
+        // Aliases mysql_deltable and mysql_subquery are chosen to be unlikely to conflict.
+        $this->execute("DELETE mysql_deltable FROM {" . $table . "} mysql_deltable JOIN " .
+                "($subquery) mysql_subquery ON mysql_subquery.$alias = mysql_deltable.$field", $params);
+    }
+
     public function sql_cast_char2int($fieldname, $text=false) {
         return ' CAST(' . $fieldname . ' AS SIGNED) ';
     }
diff --git a/lib/dml/tests/dml_test.php b/lib/dml/tests/dml_test.php
index a87c36239af..6e472b59bad 100644
--- a/lib/dml/tests/dml_test.php
+++ b/lib/dml/tests/dml_test.php
@@ -3429,6 +3429,29 @@ class core_dml_testcase extends database_driver_testcase {
         $this->assertEquals(1, $DB->count_records($tablename));
     }
 
+    public function test_delete_records_subquery() {
+        $DB = $this->tdb;
+        $dbman = $DB->get_manager();
+
+        $table = $this->get_test_table();
+        $tablename = $table->getName();
+
+        $table->add_field('id', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, XMLDB_SEQUENCE, null);
+        $table->add_field('course', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, '0');
+        $table->add_key('primary', XMLDB_KEY_PRIMARY, array('id'));
+        $dbman->create_table($table);
+
+        $DB->insert_record($tablename, array('course' => 3));
+        $DB->insert_record($tablename, array('course' => 2));
+        $DB->insert_record($tablename, array('course' => 2));
+
+        // This is not a useful scenario for using a subquery, but it will be sufficient for testing.
+        // Use the 'frog' alias just to make it clearer when we are testing the alias parameter.
+        $DB->delete_records_subquery($tablename, 'id', 'frog',
+                'SELECT id AS frog FROM {' . $tablename . '} WHERE course = ?', [2]);
+        $this->assertEquals(1, $DB->count_records($tablename));
+    }
+
     public function test_delete_records_list() {
         $DB = $this->tdb;
         $dbman = $DB->get_manager();
diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index ee4c4b0fc87..d4c5e583373 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -5277,9 +5277,8 @@ function remove_course_contents($courseid, $showfeedback = true, array $options
     // Remove all data from availability and completion tables that is associated
     // with course-modules belonging to this course. Note this is done even if the
     // features are not enabled now, in case they were enabled previously.
-    $DB->delete_records_select('course_modules_completion',
-           'coursemoduleid IN (SELECT id from {course_modules} WHERE course=?)',
-           array($courseid));
+    $DB->delete_records_subquery('course_modules_completion', 'coursemoduleid', 'id',
+            'SELECT id from {course_modules} WHERE course = ?', [$courseid]);
 
     // Remove course-module data that has not been removed in modules' _delete_instance callbacks.
     $cms = $DB->get_records('course_modules', array('course' => $course->id));
diff --git a/lib/upgrade.txt b/lib/upgrade.txt
index 709dee47def..0a363187c4b 100644
--- a/lib/upgrade.txt
+++ b/lib/upgrade.txt
@@ -1,6 +1,10 @@
 This files describes API changes in core libraries and APIs,
 information provided here is intended especially for developers.
 
+=== 3.8.6 ===
+* New DML function $DB->delete_records_subquery() to delete records based on a subquery in a way
+  that will work across databases.
+
 === 3.8.5 ===
 * The `$CFG->behat_retart_browser_after` configuration setting has been removed.
   The browser session is now restarted between all tests.