Build Your Own SQLite — Rust

A barebones SQLite implementation in Rust, built for the CodeCrafters "Build Your Own SQLite" challenge. Zero dependencies: everything (SQL parsing, B-tree traversal, record decoding) is implemented from scratch against the official SQLite file format spec, with the SQLite database file format diagrams as a supplementary document for better illustration.

What it supports

• .dbinfo and .tables dot-commands
• SELECT with column projection, SELECT *, COUNT(*)
• WHERE filtering via full table scan
• WHERE filtering via index scan (uses the index B-tree to find rowids, then point-lookups into the table B-tree)

$ ./your_program.sh companies.db "select id, name from companies where country = 'eritrea'"

What I learned

• How SQLite lays out a database file: the header, pages, B-tree page types (interior vs. leaf), and cell pointer arrays
• How indexes work in SQLite: finding rowids via the index B-tree, then rowid lookups into the table B-tree + choosing between index scan and full table scan at query time
• How to write a tokenizer + parser with an AST for SQL in Rust
• Zero-copy binary parsing in Rust with slices and methods like split_first_chunk / split_at_checked
• How varints pack a 64-bit integer into 1-9 bytes, and how SQLite's varint differs from Protocol Buffers' LEB128 (the 9th byte uses all 8 bits)

Fun detail: the implementation bootstraps itself by parsing SQLite's own sqlite_schema CREATE TABLE statement with its own parser, then uses that to decode every other table's schema.

Skeleton

File	Role
src/main.rs	CLI entry point; query planning (index scan vs. table scan)
src/sql.rs	Tokenizer + recursive-descent parser for SELECT / CREATE TABLE / CREATE INDEX
src/sqlite.rs	File format layer: pages, B-trees, varints, record decoding, schema maps
src/error.rs	Error types