CoreSQL

A small, extensible embedded database in C++20.

CoreSQL explores a simple idea: a database should be small enough to understand and structured enough to extend. It combines a typed relational core, optional SQL, and durable local files. It has no SQLite runtime dependency.

• Small and readable. About 10,000 lines across the engine, SQL frontend, public headers and bundled add-ons, including comments and blank lines; tests and external reference code are separate.
• Clear boundaries. Storage and transactions belong to the core. SQL parsing and domain-specific behavior live in separate modules.
• Extensible by design. Register types, scalar functions, aggregates and index providers. Even built-in integer, real and text types use the type-extension API. Bundled add-ons include JSON, vectors, dates, decimals, timestamps, spatial boxes and an experimental graph API.

Extensions are trusted, linked C++ code, not sandboxed or dynamically loaded plugins. The storage engine, transaction model and query operators remain part of the core. See the extension contract.

Status: early and experimental

0.1.0 is in development. CoreSQL is useful for experimentation and small local applications whose owners can accept changing interfaces and maintain backups. It is not yet a production replacement for SQLite or DuckDB.

Transactions, savepoints, indexes, crash recovery, backup/restore and a bounded SQL dialect are implemented. API/ABI and permanent file compatibility are not promised. All live data stays in RAM; the default encoded-state limit is 1 GiB, configurable at build time, not a RAM budget. A file has one owner, and calls require external serialization. Windows, a server protocol and full SQL compatibility are absent.

Read the SQL dialect, storage contract and backup/upgrade guide before keeping data you care about.

Try it

Requires CMake 3.20+, a C++20 toolchain with floating-point from_chars/to_chars, and macOS 26+ or Linux. Python 3.9+ enables the full test suite.

cmake -S . -B build/release -DCMAKE_BUILD_TYPE=Release
cmake --build build/release -j 4
ctest --test-dir build/release --output-on-failure -j 4
./build/release/coresql_persistent_sql notes.core
./build/release/coresql_sql_cli examples/sql.sql

The persistent example writes, closes and reopens its database. The CLI runs SQL scripts or reads standard input. Ordinary builds fetch no dependencies. For C++ integration, use CoreSQL::core or CoreSQL::sql through CMake; installation and examples cover the complete workflow.

Performance

The latest recorded full TPC-H Q1–Q22 comparison is a historical September 15, 2026 run at SF 0.03 (180,566 lineitems). CoreSQL completed and checked all 22 queries. SQLite completed 20: CoreSQL was faster on 12, SQLite on eight; SQLite hit the 15-second timeout on Q19 and Q21. DuckDB was faster on all 22 in that run.

These are single-thread, in-memory client timings on an Apple M1 with 16 GiB RAM: median of three measured runs after one warmup, excluding loading. Parsing, execution and fetching are included. SQLite uses adapted SQL, TEXT dates and approximate REAL decimals; CoreSQL uses native DATE/DECIMAL. Drivers also differ. This is an engineering comparison, not an official TPC-H result, a durability benchmark, or evidence of general superiority.

All 22 query times — milliseconds, lower is better

Query	CoreSQL ms	SQLite ms
Q1	175.283	90.511
Q2	21.437	19.803
Q3	32.464	48.350
Q4	19.690	37.819
Q5	39.436	70.774
Q6	29.702	11.726
Q7	64.957	56.954
Q8	34.362	129.663
Q9	57.243	158.060
Q10	24.927	18.897
Q11	5.360	25.208
Q12	30.588	23.301
Q13	38.574	46.479
Q14	20.049	11.768
Q15	20.177	11.745
Q16	8.206	10.973
Q17	13.022	801.836
Q18	62.454	75.183
Q19	14.256	Timeout (>15 s)
Q20	13.201	1251.266
Q21	600.516	Timeout (>15 s)
Q22	8.364	336.354

No speed ratio is assigned to timeouts. SQLite is the pinned 3.54.0 development baseline, not a stable-release comparison. CoreSQL was a modified working tree based on 2d3342712b; these measurements predate the current changes and are not a benchmark of the current checkout. Three trials do not establish a stable ranking for close results; Q8 also showed variability in a separate check.

Full methodology and DuckDB results · Raw measurements and fingerprints · Reproduction instructions

Explore and contribute

Guide · Examples · Architecture · Documentation · Contributing · Release readiness

CoreSQL's original contributions use the MIT license. External material retains its own notices. CoreSQL is independently maintained and is not affiliated with SQLite or DuckDB. The original development and SQLite reference history is preserved separately from the single-commit main branch; see provenance and third-party notices.