# Database > Run SQL against PostgreSQL, MySQL, or SQLite from the iii engine — reads, writes, transactions, and prepared statements over managed connection pools. - Skill: `iii-hq/database` (Agent Skill) - Install (CLI): `npx skillmds@latest add iii-hq/database` - Raw SKILL.md: https://api.skillmd.com/api/skills/iii-hq/database/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Data & Analytics - Author: iii-hq (https://skillmd.com/u/iii-hq) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/iii-hq/database --- # database The database worker connects to PostgreSQL, MySQL, and SQLite through a managed per-database connection pool. Every callable surface lives under the `database::*` namespace. The driver is chosen from each database URL scheme (`sqlite:`, `postgres://`, `postgresql://`, `mysql://`). Runtime settings live in the `configuration` worker under id `database`; pools hot-reload when the value changes. SQLite is the recommended starting point. Placeholder syntax: `?` for SQLite and MySQL, `$1`/`$2`/… for Postgres. ## When to Use - You need to read rows from a configured database (`database::query`). - You need to insert, update, delete, or run DDL and read affected-row counts or autoincrement ids (`database::execute`). - Several statements must commit or roll back together as one unit (`database::transaction`, `database::executeBatch`, or the interactive transaction surface). - The same parameterized SQL will run many times and you want to skip per-call parse/plan cost (`database::prepareStatement` + `database::runStatement`). - You need read-your-writes across round-trips with logic between steps (`database::beginTransaction` … `commitTransaction` / `rollbackTransaction`). ## Boundaries - Not a migration tool, ORM, or schema designer — pass raw SQL only. - Not a general pub/sub bus. `database::row-changed` reports only what THIS worker wrote, on commit — not change data capture; a write from psql or another worker is invisible to it. - `database::query` is read-oriented; use `database::execute` for writes. Running a SELECT through `execute` discards rows. - Prepared handles pin a pool connection until TTL expiry — not transactions. Batch `database::transaction` / `database::executeBatch` need every statement up front; use the interactive surface when code must branch between steps. - MySQL ignores the `returning` option on `execute` (warn-once). SQLite degrades `read_committed` / `repeatable_read` isolation to serializable. - For filesystem or shell operations, use the `shell` worker instead. ## Functions - `database::query` — run read-only SQL and return rows, row count, and column metadata. - `database::execute` — run write SQL (INSERT/UPDATE/DELETE/DDL) and return affected rows, optional last insert id, and optional RETURNING rows. - `database::executeBatch` — convenience form of `transaction`: statements may be bare SQL strings or `{sql, params}` objects (prefer `params` for dynamic values). Same atomic semantics, envelope, and `failed_index` reporting as `transaction`. - `database::prepareStatement` — parse and plan SQL once; return a handle that pins a pool connection until TTL expiry. - `database::runStatement` — re-execute a prepared handle with new bind params; response shape matches `query`. - `database::transaction` — run an ordered batch of statements atomically; rolls back on first failure and reports `failed_index`. - `database::beginTransaction` — open an interactive transaction and return an id plus expiry deadline. - `database::transactionQuery` — read SQL inside an open interactive transaction; same envelope as `query`. - `database::transactionExecute` — write SQL inside an open interactive transaction; same envelope as `execute`. Rejects bare transaction-control SQL — finalize via `commitTransaction` or `rollbackTransaction`. - `database::commitTransaction` — commit and finalize an interactive transaction. - `database::rollbackTransaction` — roll back and finalize an interactive transaction. - `database::listDatabases` — every configured database with its driver, credential-redacted URL, pool settings and TLS mode. Config only; use `database::health` for live state. Interactive transactions auto-roll back when `timeout_ms` elapses (default 30 s, max 5 min). Prepared handles default to a 1 h TTL (max 24 h) with no explicit release call — let them expire or stop using them when done. ### Reading the schema One shape across all three drivers — prefer these over hand-writing `sqlite_master` / `information_schema` / `PRAGMA`. - `database::listTables` — tables and views, with kind and (postgres) schema. - `database::describeTable` — columns with type, nullability, default, primary key and a structured `foreign_key` of `{ schema, table, column }`; plus indexes and a planner row estimate. - `database::describeSchema` — the same for every table in one pass. Use this rather than looping `describeTable`. - `database::schemaDiagram` — positioned nodes, routed foreign-key edges, hub `degree` and `isolated` tables. For reasoning about a schema's shape, not only for drawing it. ### Reading data - `database::browseTable` — paged, sorted, filtered reads with no SQL. Filters are `{ column, op, value }` and `total` honours them. Follow a foreign key with an equality filter at `page_size: 1`. - `database::explain` — the plan as a tree with costs and warnings. `analyze` **runs** the statement, so it defaults to false and is refused for anything that is not a single read. - `database::columnStats` — planner statistics by default (approximate, labelled `source: planner`); `exact: true` scans. To profile rows you already hold, use the `fp` worker on a `browseTable` result instead. ### Operations and reuse - `database::health` — pool occupancy, active queries, table sizes, locks, cache ratio. Each section is `available`, `unsupported` or `denied`, so a driver gap is never mistaken for an empty result. - `database::terminateQuery` — end a session, or cancel its statement with `cancel_only`. Takes an id from `database::health`. - `database::saveQuery`, `database::listSavedQueries`, `database::deleteSavedQuery` — named queries per database, kept in the `state` worker. - `database::history` — recent queries, newest first. Best effort, not an audit log; bind `database::row-changed` for that. ## Reacting to writes Register a `database::row-changed` trigger to be told when this worker commits a change, instead of polling: ```json { "trigger_type": "database::row-changed", "config": { "db": "primary", "table": "orders", "ops": ["insert"] } } ``` The event is `{ db, table, op, affected_rows, returning?, at }`. It fires on commit — an interactive transaction's writes are announced by `commitTransaction`, and a rollback announces nothing. `table` is null when the statement's table cannot be read off the SQL (a CTE-wrapped write), and `runStatement` does not fire because it has no affected-row count to report. Delivery is best-effort: it is not durable with the commit and has no replay or exactly-once guarantee.