A CPV code is now stored once, keeping its longest description

internal/store/migrations/00010_unique_cpv_codes.sql

@@ -0,0 +1,60 @@
+-- +goose Up
+-- +goose StatementBegin
+-- A CPV code has one official description, so it is now one row whatever
+-- description it arrives with: EU Supply cuts descriptions to 64 characters,
+-- which made a second row for each code it sent. The duplicates are merged
+-- into the row with the longest description, and the upsert keeps the
+-- longest from now on. Other schemes still get a row per distinct content.
+
+-- The row each CPV row merges into.
+CREATE TEMP TABLE "cpv_merge" AS
+SELECT
+	"c"."id" AS "id",
+	(
+		SELECT "k"."id" FROM "classification_codes" "k"
+		WHERE "k"."is_cpv" AND "k"."code" = "c"."code"
+		ORDER BY length("k"."classification") DESC, "k"."id"
+		LIMIT 1
+	) AS "keep_id"
+FROM "classification_codes" "c"
+WHERE "c"."is_cpv";
+
+-- An opportunity linked to both rows keeps only its link to the kept one.
+DELETE FROM "opportunity_classifications"
+WHERE "classification_id" IN (
+	SELECT "id" FROM "cpv_merge" WHERE "id" <> "keep_id"
+)
+AND EXISTS (
+	SELECT 1
+	FROM "cpv_merge" "m"
+	JOIN "opportunity_classifications" "kept"
+		ON "kept"."classification_id" = "m"."keep_id"
+	WHERE "m"."id" = "opportunity_classifications"."classification_id"
+		AND "kept"."opportunity_uuid"
+			= "opportunity_classifications"."opportunity_uuid"
+);
+
+UPDATE "opportunity_classifications"
+SET "classification_id" = (
+	SELECT "keep_id" FROM "cpv_merge"
+	WHERE "id" = "opportunity_classifications"."classification_id"
+)
+WHERE "classification_id" IN (
+	SELECT "id" FROM "cpv_merge" WHERE "id" <> "keep_id"
+);
+
+DELETE FROM "classification_codes"
+WHERE "id" IN (SELECT "id" FROM "cpv_merge" WHERE "id" <> "keep_id");
+
+DROP TABLE "cpv_merge";
+
+CREATE UNIQUE INDEX IF NOT EXISTS "classification_codes_cpv"
+	ON "classification_codes" ("code") WHERE "is_cpv";
+-- +goose StatementEnd
+
+-- +goose Down
+-- +goose StatementBegin
+-- The merged duplicates aren't restored: they only differed by a cut-off
+-- description.
+DROP INDEX IF EXISTS "classification_codes_cpv";
+-- +goose StatementEnd