DuckDB UI vs HSQLDB

DuckDB UI is a free browser interface for a local DuckDB instance, added through the ui extension. Start it with `duckdb -ui` or `CALL start_ui()`; it opens in the default browser and is served by an HTTP server embedded in DuckDB, available by default at `http://localhost:4213`. The interface includes a SQL notebook with autocomplete and keyboard shortcuts, a catalog browser, a table explorer with column statistics, and a results viewer with sorting and filtering. The native DuckDB process gives it access to local cores, memory, and files. Queries run locally by default, and queries and data stay on the computer. Connecting to MotherDuck is optional and requires signing in. The UI is built and maintained by MotherDuck. The local server retrieves interface files from ui.duckdb.org, so alternate configured URLs should be trusted because the application can access loaded DuckDB data. The UI cannot be run directly against a read-only database and does not currently support windows_arm64.

HSQLDB is a Java-based relational database engine for embedded or server use, with both in-memory and disk-based tables. It supports SQL:2023 core features and many optional features, plus lock-based and MVCC transaction models; the engine is fully multithreaded. Listed capabilities include JSON constructor functions, CSV loading and unloading, temporal system-versioned tables, row-level access control, and log-based replica synchronization. It includes a command-line SQL tool and simple GUI query tools. The latest official release listed is version 2.7.4, compatible with JDK 8 and above, and packages include Java 11 module jars as well as Java 8 jars for HSQLDB and SQL Tool. HSQLDB is self-hosted, with high availability, read replicas, and JSON data support listed. Its default combined limit for CACHED tables is 8TB, extendable to 256TB with a connection property; each TEXT table is limited to 256GB, and memory tables depend on available memory. The software is free to use in commercial products when license terms are met; its licenses are based on the new BSD License. The HSQLDB plan is free. A Developer subscription is $100 a year; Premier Corporate is $2,500 a year at the base level. Support options include community channels and paid commercial support.