Step by step examples to teach you SQL Parser.

Learn SQL Parser implementation via these examples.

1. sqlparser-rs

Extensible SQL Lexer and Parser for Rust.

SQL Parser Tutorial

The goal of this project is to build a SQL lexer and parser capable of parsing SQL that conforms with the ANSI/ISO SQL standard while also making it easy to support custom dialects so that this crate can be used as a foundation for vendor-specific parsers.

This parser is currently being used by the DataFusion query engine, LocustDB, Ballista and GlueSQL.

Example

To parse a simple SELECT statement:

use sqlparser::dialect::GenericDialect;
use sqlparser::parser::Parser;

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

let dialect = GenericDialect {}; // or AnsiDialect, or your own dialect ...

let ast = Parser::parse_sql(&dialect, sql).unwrap();

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

This outputs

AST: [Query(Query { ctes: [], body: Select(Select { distinct: false, projection: [UnnamedExpr(Identifier("a")), UnnamedExpr(Identifier("b")), UnnamedExpr(Value(Long(123))), UnnamedExpr(Function(Function { name: ObjectName(["myfunc"]), args: [Identifier("b")], over: None, distinct: false }))], from: [TableWithJoins { relation: Table { name: ObjectName(["table_1"]), alias: None, args: [], with_hints: [] }, joins: [] }], selection: Some(BinaryOp { left: BinaryOp { left: Identifier("a"), op: Gt, right: Identifier("b") }, op: And, right: BinaryOp { left: Identifier("b"), op: Lt, right: Value(Long(100)) } }), group_by: [], having: None }), order_by: [OrderByExpr { expr: Identifier("a"), asc: Some(false) }, OrderByExpr { expr: Identifier("b"), asc: None }], limit: None, offset: None, fetch: None })]

Command line

To parse a file and dump the results as JSON:

$ cargo run --features json_example --example cli FILENAME.sql [--dialectname]

Supporting custom SQL dialects

This is a work in progress, but we have some notes on writing a custom SQL parser.

Design

The core expression parser uses the Pratt Parser design, which is a top-down operator-precedence (TDOP) parser, while the surrounding SQL statement parser is a traditional, hand-written recursive descent parser. Eli Bendersky has a good tutorial on TDOP parsers, if you are interested in learning more about the technique.

Full Example

Let us look at a full SQL Parser Example.

Step 1. Write Code

Finally we need to write our code as follows:

(a). cli.rs


#![warn(clippy::all)]

/// A small command-line app to run the parser.
/// Run with `cargo run --example cli`
use std::fs;

use simple_logger::SimpleLogger;
use sqlparser::dialect::*;
use sqlparser::parser::Parser;

fn main() {
    SimpleLogger::new().init().unwrap();

    let filename = std::env::args().nth(1).expect(
        r#"
No arguments provided!

Usage:
$ cargo run --example cli FILENAME.sql [--dialectname]

To print the parse results as JSON:
$ cargo run --feature json_example --example cli FILENAME.sql [--dialectname]

"#,
    );

    let dialect: Box<dyn Dialect> = match std::env::args().nth(2).unwrap_or_default().as_ref() {
        "--ansi" => Box::new(AnsiDialect {}),
        "--bigquery" => Box::new(BigQueryDialect {}),
        "--postgres" => Box::new(PostgreSqlDialect {}),
        "--ms" => Box::new(MsSqlDialect {}),
        "--mysql" => Box::new(MySqlDialect {}),
        "--snowflake" => Box::new(SnowflakeDialect {}),
        "--hive" => Box::new(HiveDialect {}),
        "--redshift" => Box::new(RedshiftSqlDialect {}),
        "--generic" | "" => Box::new(GenericDialect {}),
        s => panic!("Unexpected parameter: {}", s),
    };

    println!("Parsing from file '{}' using {:?}", &filename, dialect);
    let contents = fs::read_to_string(&filename)
        .unwrap_or_else(|_| panic!("Unable to read the file {}", &filename));
    let without_bom = if contents.chars().next().unwrap() as u64 != 0xfeff {
        contents.as_str()
    } else {
        let mut chars = contents.chars();
        chars.next();
        chars.as_str()
    };
    let parse_result = Parser::parse_sql(&*dialect, without_bom);
    match parse_result {
        Ok(statements) => {
            println!(
                "Round-trip:n'{}'",
                statements
                    .iter()
                    .map(std::string::ToString::to_string)
                    .collect::<Vec<_>>()
                    .join("n")
            );

            if cfg!(feature = "json_example") {
                #[cfg(feature = "json_example")]
                {
                    let serialized = serde_json::to_string_pretty(&statements).unwrap();
                    println!("Serialized as JSON:n{}", serialized);
                }
            } else {
                println!("Parse results:n{:#?}", statements);
            }

            std::process::exit(0);
        }
        Err(e) => {
            println!("Error during parsing: {:?}", e);
            std::process::exit(1);
        }
    }
}

(b). parse_select.rs

#![warn(clippy::all)]

use sqlparser::dialect::GenericDialect;
use sqlparser::parser::*;

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

    let dialect = GenericDialect {};

    let ast = Parser::parse_sql(&dialect, sql).unwrap();

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

Reference

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