Switch to storing Git repositories in a table

Rather than just storing the URL in the guix_revisions and
load_new_guix_revision_jobs tables. This will help when storing more
information like tags and branches in the future.

sqitch/deploy/git_repositories.sql

@@ -0,0 +1,41 @@
+-- Deploy guix-data-service:git_repositories to pg
+-- requires: initial_import
+
+BEGIN;
+
+CREATE TABLE git_repositories (
+    id integer PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
+    label character varying,
+    url character varying NOT NULL UNIQUE
+);
+
+INSERT INTO git_repositories (url)
+SELECT DISTINCT url FROM guix_revisions;
+
+-- Change the guix_revisions table
+
+ALTER TABLE guix_revisions ADD COLUMN git_repository_id integer
+REFERENCES git_repositories (id);
+
+UPDATE guix_revisions SET git_repository_id = (
+  SELECT id FROM git_repositories WHERE guix_revisions.url = git_repositories.url
+);
+
+ALTER TABLE guix_revisions ALTER COLUMN git_repository_id SET NOT NULL;
+
+ALTER TABLE guix_revisions DROP COLUMN url;
+
+-- Change the load_new_guix_revision_jobs table
+
+ALTER TABLE load_new_guix_revision_jobs ADD COLUMN git_repository_id integer
+REFERENCES git_repositories (id);
+
+UPDATE load_new_guix_revision_jobs SET git_repository_id = (
+  SELECT id FROM git_repositories WHERE load_new_guix_revision_jobs.url = git_repositories.url
+);
+
+ALTER TABLE load_new_guix_revision_jobs ALTER COLUMN git_repository_id SET NOT NULL;
+
+ALTER TABLE load_new_guix_revision_jobs DROP COLUMN url;
+
+COMMIT;