Jobs.jobset_id: make not-null

src/sql/hydra.sql

@@ -146,7 +146,7 @@ create table JobsetInputAlts (
 create table Jobs (
     project       text not null,
     jobset        text not null,
-    jobset_id     integer null,
+    jobset_id     integer not null,
     name          text not null,
 
     primary key   (project, jobset, name),

src/sql/upgrade-63.sql

@@ -0,0 +1,7 @@
+-- Make the Jobs.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 Jobs
+  ALTER COLUMN jobset_id SET NOT NULL;