tag	d9972b8ddc1c6f2f986e7e650ea1a1fe71d894c6
tagger	Andy Grove <andygrove73@gmail.com>	Sat Sep 08 07:24:40 2018 -0600
object	ed40edd3b04f7bdeaadc68e29601d914b646386f

commit	ed40edd3b04f7bdeaadc68e29601d914b646386f	[log] [tgz]
author	Andy Grove <andygrove73@gmail.com>	Sat Sep 08 07:24:32 2018 -0600
committer	Andy Grove <andygrove73@gmail.com>	Sat Sep 08 07:24:32 2018 -0600
tree	a6accc1f6b93dcc315ea6573c60216df40901c97
parent	9cc4bc3423c3a7ac4fdd360b623e4234032b60e9 [diff]

tree: a6accc1f6b93dcc315ea6573c60216df40901c97

README.md

ANSI SQL Lexer and Parser for Rust

The primary goal of this project is to build a SQL lexer and parser capable of parsing SQL that conforms with the ANSI SQL:2011 standard.

A secondary goal is to make it easy for others to use this library as a foundation for building custom SQL parsers for vendor-specific dialects.

This parser is currently being used by the DataFusion query engine.

Example

The current code is capable of parsing some trivial SELECT and CREATE TABLE statements.

let sql = "SELECT a, b, 123, myfunc(b) \
    FROM table_1 \
    WHERE a > b AND b < 100 \
    ORDER BY a DESC, b";

let ast = Parser::parse_sql(sql.to_string()).unwrap();

println!("AST: {:?}", ast);

This outputs

AST: SQLSelect { projection: [SQLIdentifier("a"), SQLIdentifier("b"), SQLLiteralLong(123), SQLFunction { id: "myfunc", args: [SQLIdentifier("b")] }], relation: Some(SQLIdentifier("table_1")), selection: Some(SQLBinaryExpr { left: SQLBinaryExpr { left: SQLIdentifier("a"), op: Gt, right: SQLIdentifier("b") }, op: And, right: SQLBinaryExpr { left: SQLIdentifier("b"), op: Lt, right: SQLLiteralLong(100) } }), order_by: Some([SQLOrderBy { expr: SQLIdentifier("a"), asc: false }, SQLOrderBy { expr: SQLIdentifier("b"), asc: true }]), group_by: None, having: None, limit: None }

Design

This parser is implemented using the Pratt Parser design, which is a top-down operator-precedence parser.

I am a fan of this design pattern over parser generators for the following reasons:

Code is simple to write and can be concise and elegant (this is far from true for this current implementation unfortunately, but I hope to fix that using some macros)
Performance is generally better than code generated by parser generators
Debugging is much easier with hand-written code
It is far easier to extend and make dialect-specific extensions compared to using a parser generator

Supporting custom SQL dialects

This is a work in progress but I started some notes on writing a custom SQL parser.

Contributing

Contributors are welcome! Please see the current issues and feel free to file more!