migrations: more database migrations for various database fixes

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I8567eec6980b2b5453687bcbd07a61206a6a6964

migrations/postgres/V9__fix_indexes_and_constraints.sql

@@ -0,0 +1,26 @@
+-- Drop redundant indexes (already covered by UNIQUE constraints)
+DROP INDEX IF EXISTS idx_users_username;
+DROP INDEX IF EXISTS idx_user_libraries_user_id;
+
+-- Add missing indexes for comments table
+CREATE INDEX IF NOT EXISTS idx_comments_media ON comments(media_id);
+CREATE INDEX IF NOT EXISTS idx_comments_parent ON comments(parent_comment_id);
+
+-- Remove duplicates before adding unique constraint
+DELETE FROM external_metadata e1
+WHERE EXISTS (
+    SELECT 1 FROM external_metadata e2
+    WHERE e1.media_id = e2.media_id
+    AND e1.source = e2.source
+    AND e1.ctid < e2.ctid
+);
+
+-- Add unique constraint for external_metadata (idempotent)
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_constraint WHERE conname = 'uq_external_metadata_source'
+    ) THEN
+        ALTER TABLE external_metadata ADD CONSTRAINT uq_external_metadata_source UNIQUE(media_id, source);
+    END IF;
+END $$;