106798: update migration for H2

dspace-api/src/main/resources/org/dspace/storage/rdbms/sqlmigration/h2/V7.6_2024.12.17__workspaceitem_add_item_id_unique_constraint.sql

@@ -7,15 +7,15 @@
 --
 
 -- In the workspaceitem table, if there are multiple rows referring to the same item ID, keep only the first of them.
-WITH dedup AS (
-    SELECT item_id, MIN(workspace_item_id) AS workspace_item_id
+DELETE FROM workspaceitem WHERE EXISTS (
+    SELECT item_id
     FROM workspaceitem
     GROUP BY item_id
     HAVING COUNT(workspace_item_id) > 1
-)
-DELETE FROM workspaceitem
-    USING dedup
-WHERE workspaceitem.item_id = dedup.item_id AND workspaceitem.workspace_item_id <> dedup.workspace_item_id;
-
+) AND workspaceitem.workspace_item_id NOT IN (
+    SELECT MIN(workspace_item_id) AS workspace_item_id
+    FROM workspaceitem
+    GROUP BY item_id
+);
 -- Identify which rows have duplicates, and compute their replacements.
 ALTER TABLE workspaceitem ADD CONSTRAINT unique_item_id UNIQUE(item_id);