Builds.jobset_id: make not-null

src/sql/hydra.sql

@@ -170,7 +170,7 @@ create table Builds (
     -- Info about the inputs.
     project       text not null,
     jobset        text not null,
-    jobset_id     integer null,
+    jobset_id     integer not null,
     job           text not null,
 
     -- Info about the build result.

src/sql/upgrade-64.sql

@@ -0,0 +1,7 @@
+-- Make the Builds.jobset_id column NOT NULL. If this upgrade fails,
+-- either the admin didn't run the backfiller or there is a bug. If
+-- the admin ran the backfiller and there are null columns, it is
+-- very important to figure out where the nullable columns came from.
+
+ALTER TABLE Builds
+  ALTER COLUMN jobset_id SET NOT NULL;