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f82dc74e38
...and add a `rustfmt.toml` as advised in https://www.reddit.com/r/rust/comments/9jl6a9/pro_tip_if_you_use_cargo_fmtrustfmt_use_a/
55 lines
3.5 KiB
Markdown
55 lines
3.5 KiB
Markdown
# Extensible SQL Lexer and Parser for Rust
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[](https://opensource.org/licenses/Apache-2.0)
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[](https://crates.io/crates/sqlparser)
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[](https://travis-ci.org/andygrove/sqlparser-rs)
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[](https://coveralls.io/github/andygrove/sqlparser-rs?branch=master)
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[](https://gitter.im/sqlparser-rs/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
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The goal of this project is to build a SQL lexer and parser capable of parsing SQL that conforms with the [ANSI SQL:2011](https://jakewheat.github.io/sql-overview/sql-2011-foundation-grammar.html#_5_1_sql_terminal_character) standard but also making it easy to support custom dialects so that this crate can be used as a foundation for vendor-specific parsers.
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This parser is currently being used by the [DataFusion](https://github.com/andygrove/datafusion) query engine and [LocustDB](https://github.com/cswinter/LocustDB).
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## Example
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The current code is capable of parsing some trivial SELECT and CREATE TABLE statements.
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```rust
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let sql = "SELECT a, b, 123, myfunc(b) \
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FROM table_1 \
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WHERE a > b AND b < 100 \
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ORDER BY a DESC, b";
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let dialect = GenericSqlDialect{}; // or AnsiSqlDialect, or your own dialect ...
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let ast = Parser::parse_sql(&dialect,sql.to_string()).unwrap();
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println!("AST: {:?}", ast);
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```
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This outputs
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```rust
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AST: [SQLSelect(SQLQuery { ctes: [], body: Select(SQLSelect { distinct: false, projection: [UnnamedExpression(SQLIdentifier("a")), UnnamedExpression(SQLIdentifier("b")), UnnamedExpression(SQLValue(Long(123))), UnnamedExpression(SQLFunction { name: SQLObjectName(["myfunc"]), args: [SQLIdentifier("b")], over: None })], relation: Some(Table { name: SQLObjectName(["table_1"]), alias: None }), joins: [], selection: Some(SQLBinaryExpr { left: SQLBinaryExpr { left: SQLIdentifier("a"), op: Gt, right: SQLIdentifier("b") }, op: And, right: SQLBinaryExpr { left: SQLIdentifier("b"), op: Lt, right: SQLValue(Long(100)) } }), group_by: None, having: None }), order_by: Some([SQLOrderByExpr { expr: SQLIdentifier("a"), asc: Some(false) }, SQLOrderByExpr { expr: SQLIdentifier("b"), asc: None }]), limit: None })]
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```
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## Design
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This parser is implemented using the [Pratt Parser](https://tdop.github.io/) design, which is a top-down operator-precedence parser.
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I am a fan of this design pattern over parser generators for the following reasons:
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- 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)
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- Performance is generally better than code generated by parser generators
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- Debugging is much easier with hand-written code
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- It is far easier to extend and make dialect-specific extensions compared to using a parser generator
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## Supporting custom SQL dialects
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This is a work in progress but I started some notes on [writing a custom SQL parser](docs/custom_sql_parser.md).
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## Contributing
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Contributors are welcome! Please see the [current issues](https://github.com/andygrove/sqlparser-rs/issues) and feel free to file more!
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Please run [cargo fmt](https://github.com/rust-lang/rustfmt#on-the-stable-toolchain) to ensure the code is properly formatted.
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