diff --git a/svc/db/migrations/2026-06-18_zbggcampaign_nullable_campaign.sql b/svc/db/migrations/2026-06-18_zbggcampaign_nullable_campaign.sql
new file mode 100644
index 0000000..fee254e
--- /dev/null
+++ b/svc/db/migrations/2026-06-18_zbggcampaign_nullable_campaign.sql
@@ -0,0 +1,7 @@
+-- Allow "clear campaign" actions by permitting NULL sdcampaign_id.
+-- The app models campaign history as append-only rows; a NULL sdcampaign_id
+-- represents "no campaign assigned" for that variant at that point in time.
+
+ALTER TABLE zbggcampaign
+  ALTER COLUMN sdcampaign_id DROP NOT NULL;
+