storage-engine-playground/crates/query-ops/tests/hand_plan.rs

//! Hand-written query plan composed from `scan_atom`, `semijoin`, and `natural_join`.
//!
//! Schema:
//! - `author(name, book)`: who wrote each book
//! - `bestseller(book)`: the set of bestseller titles
//! - `price(book, dollars)`: price of each book
//!
//! Rule:
//! - `Q(name, book, dollars) :- author(name, book), bestseller(book), price(book, dollars).`
//!   ("Authors of bestsellers along with each book's price.")
//!
//! The plan first scans each input table, then narrows `author` to authors of
//! bestsellers via a semijoin against `bestseller`, then attaches each book's
//! price via a natural join against `price`.

use query_ops::atom::{AtomPattern, Term, scan_atom};
use query_ops::join::{natural_join, semijoin};
use storage::table::Table;
use storage::value::Value;

fn s(x: &str) -> Value {
    Value::Str(x.to_string())
}

fn i(x: i64) -> Value {
    Value::Int(x)
}

#[test]
fn authors_of_bestsellers_with_price() {
    let author = Table::from_rows(
        2,
        vec![
            vec![s("Ursula K. Le Guin"), s("A Wizard of Earthsea")],
            vec![s("Toni Morrison"), s("Beloved")],
            vec![s("Ursula K. Le Guin"), s("The Left Hand of Darkness")],
            vec![s("Terry Pratchett"), s("Mort")],
        ],
    );
    let bestseller = Table::from_rows(
        1,
        vec![
            vec![s("A Wizard of Earthsea")],
            vec![s("The Left Hand of Darkness")],
        ],
    );
    let price = Table::from_rows(
        2,
        vec![
            vec![s("A Wizard of Earthsea"), i(14)],
            vec![s("Beloved"), i(17)],
            vec![s("The Left Hand of Darkness"), i(15)],
            vec![s("Mort"), i(12)],
        ],
    );

    let author_rel = scan_atom(
        &author,
        &AtomPattern {
            columns: vec![Term::Var("name".to_string()), Term::Var("book".to_string())],
        },
    );
    let bestseller_rel = scan_atom(
        &bestseller,
        &AtomPattern {
            columns: vec![Term::Var("book".to_string())],
        },
    );
    let price_rel = scan_atom(
        &price,
        &AtomPattern {
            columns: vec![
                Term::Var("book".to_string()),
                Term::Var("dollars".to_string()),
            ],
        },
    );

    let authors_of_bestsellers = semijoin(&author_rel, &bestseller_rel);
    let result = natural_join(&authors_of_bestsellers, &price_rel);

    assert_eq!(
        result.columns,
        vec![
            "name".to_string(),
            "book".to_string(),
            "dollars".to_string()
        ],
    );
    assert_eq!(
        result.rows,
        vec![
            vec![s("Ursula K. Le Guin"), s("A Wizard of Earthsea"), i(14)],
            vec![
                s("Ursula K. Le Guin"),
                s("The Left Hand of Darkness"),
                i(15)
            ],
        ],
    );
}