Deduplicate passwords in database migration

db/migrations/1908210505_add_unique_index_sPassword_on_groups.sql

@@ -1,5 +1,22 @@
 -- +migrate Up
 UPDATE `groups` SET `sPassword` = NULL WHERE `sPassword` = '';
+
+# Deduplicate groups.sPassword: appends a suffix to make all sPassword unique.
+UPDATE `groups`
+  JOIN (
+    SELECT `ID`, ROW_NUMBER() OVER (PARTITION BY `groups`.`sPassword` ORDER BY `ID`) AS `order`
+    FROM `groups`
+           JOIN (
+      SELECT `ID`, `sPassword` FROM `groups` AS `groups1`
+      WHERE EXISTS(
+        SELECT `ID` from `groups` AS `groups2`
+        WHERE `groups1`.`sPassword`=`groups2`.`sPassword` AND `groups1`.`ID` > `groups2`.`ID`
+      )
+      GROUP BY `ID`
+    ) AS `duplicates` USING (`ID`)
+  ) AS `orders` USING (`ID`)
+SET `groups`.`sPassword` = CONCAT(`groups`.`sPassword`, '@dup', `orders`.`order`);
+
 ALTER TABLE `groups` ADD UNIQUE INDEX `sPassword` (`sPassword`);
 
 -- +migrate Down