DevFoundry/.devfoundry/rules/database-sql.md

Database Guidelines (Access, SQLite, SQL Server, Postgres)

1. MS Access (.mdb / .accdb):
   • Use correct date literals (#YYYY-MM-DD#).
   • Escape field names with square brackets (e.g., [Order Date]).
   • Concurrency (web apps with multiple ASP sessions writing to the same file):
     • Never hold a connection open across requests (no connection cached in Session/Application scope) — acquire it at the start of the request and close it at the end, so locks are held for the shortest possible time. See .devfoundry/references/asp-classic-framework.md for how the RouteKit DAL()/DatabaseConnection() pair already does this per-request.
     • Wrap multi-statement writes in a transaction (BeginTransaction/CommitTransaction/RollbackTransaction) so a lock conflict can't leave a partial write.
     • On a write that fails with an Access lock-conflict error (e.g. 3260 “Could not update; currently locked”, 3197, 3218 “Couldn't update; currently locked by another session”), retry with a short backoff (e.g. 3 attempts, increasing delay) before surfacing the error — do not retry silently forever.
     • Run structural/batch/migration operations (ALTER TABLE, bulk UPDATE/DELETE, Migrator_Class runs) during a maintenance window with no concurrent user traffic; table-level locking during DDL can starve concurrent requests even with retries.
2. Cross-Engine Dialect Awareness:
   • Access: TOP n, IIF(), string concatenation with &
   • SQLite: LIMIT n, IFNULL(), string concatenation with ||
   • SQL Server: TOP (n), ISNULL(), CONCAT()
   • Postgres: LIMIT n, COALESCE(), ||, boolean literals (TRUE/FALSE)
3. Parameterization: Always use parameterized queries regardless of engine.
4. Migrations: Every schema change must include a rollback/backward-compatibility note in the spec.