Build a Typed Database Expression Engine in Rust

A hand-written loop for one integer function is easy. It stops scaling when the engine must also borrow strings without copying, preserve nulls, read several column encodings, coerce types, and select functions at runtime.

This course builds the type families and checked boundaries that move those decisions out of each row loop. The result is a small vectorized expression engine whose generic code has a visible payoff: new types, operators, and arities reuse the same execution path.

Read the published course. Work through the chapters in order; each chapter extends the same starter and keeps earlier supplied tests green. The book's SUMMARY.md is the sole ordered chapter list.

• Connect logical types, owned values, borrowed values, physical arrays, and checked erased enums.
• Read nullable arrays, constants, and Indexed views without materializing a new column.
• Apply unary, binary, and ternary scalar functions through generic, erased, and bound interfaces.
• Promote supported numeric pairs for +, -, *, /, comparisons, and string contains.
• Represent one-level Lists with checked offsets and independent outer and child nullability.
• Preserve the same results and errors through one representative fast path and a batch-level asynchronous adapter.

The course deliberately stops short of Decimal arithmetic, casts, and rounding, implicit narrowing or lossy casts, nested or list-producing functions, concrete four- and five-input builtins, exhaustive fast paths, an aggregate engine, and per-row futures.

You should know ordinary Cargo use, enums, traits, references, and Option. Follow the environment setup, then work only in type-exercise-starter:

git fetch origin
git switch --create course-work --track origin/main
cargo check -p type-exercise-starter --lib --locked

Choose another branch name if course-work already exists. The starter baseline should compile. Do not inspect type-exercise/ or archived/ while solving an exercise.

Copy the cumulative supplied contract when you are ready to start a chapter:

cargo x copy-test --chapter 1
cargo test -p type-exercise-starter chapter_1 --locked

The first focused run should fail because the new behavior is missing. Read the copied destination under type-exercise-starter/src/tests/, implement the named API in other starter files, and rerun the same command until it passes. Never edit copied tests or src/tests.rs; keep all earlier copied chapters green.

Join skyzh's Discord server for discussion. For a concrete bug or improvement, open an issue or pull request.

The source code is licensed under Apache 2.0. See LICENSE. The mdBook text is © 2022-2026 Alex Chi Z and licensed under CC BY-NC-SA 4.0.