Fixed #3367 MySQL 5.7 error when ensuring discount sort order

CHANGELOG.md

@@ -2,7 +2,9 @@
 
 ## Unreleased
 
+- Fixed a SQL error that could occur when updating to Commerce 4.4.0 on MySQL. ([#3367](https://github.com/craftcms/commerce/issues/3367))
 - Fixed a PHP error that occurred when saving a discount. ([#3364](https://github.com/craftcms/commerce/issues/3364))
+
 ## 4.4.0 - 2024-01-11
 
 - Craft Commerce now requires Craft CMS 4.6.0 or later.

src/services/Discounts.php

@@ -879,8 +879,12 @@ public function ensureSortOrder(): void
         } else {
             $sql = <<<SQL
 UPDATE $table a
-JOIN (SELECT id, [[sortOrder]], ROW_NUMBER() OVER (ORDER BY [[sortOrder]] ASC, id ASC) as rownumber
-FROM $table) b ON a.id = b.id
+JOIN (
+    SELECT id, [[sortOrder]], (@ROW_NUMBER := @ROW_NUMBER + 1) as rownumber
+    FROM $table,
+    (SELECT @ROW_NUMBER := 0) AS X
+    ORDER BY [[sortOrder]] ASC, id ASC    
+) b ON a.id = b.id
 SET [[a.sortOrder]] = b.rownumber
 SQL;
         }