First pass implementation of an SQLite backing store for fetched opportunities

internal/store/migrations/00004_create_classification_codes_table.sql

@@ -0,0 +1,26 @@
+-- +goose Up
+-- +goose StatementBegin
+-- Shared, write-once lookup of classifications. A row is reused only when
+-- every content column matches; any difference (e.g. a changed description)
+-- creates a new row.
+--
+-- When adding a new scheme flag column (e.g. "is_unspsc"), the same migration
+-- must drop and recreate "classification_codes_content" with the new column
+-- included, otherwise rows differing only by that flag would be merged.
+CREATE TABLE IF NOT EXISTS "classification_codes" (
+	"id" INTEGER PRIMARY KEY,
+	"is_cpv" BOOLEAN NOT NULL,
+	"code" TEXT NOT NULL,
+	"classification" TEXT NOT NULL
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS "classification_codes_content"
+	ON "classification_codes" ("is_cpv", "code", "classification");
+CREATE INDEX IF NOT EXISTS "classification_codes_code"
+	ON "classification_codes" ("code");
+-- +goose StatementEnd
+
+-- +goose Down
+-- +goose StatementBegin
+DROP TABLE IF EXISTS "classification_codes";
+-- +goose StatementEnd