92 lines
2.5 KiB
Rust
92 lines
2.5 KiB
Rust
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//! Hand-written query plan composed from `scan_atom`, `semijoin`, and `natural_join`.
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//!
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//! Schema:
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//! - `author(name, book)`: who wrote each book
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//! - `bestseller(book)`: the set of bestseller titles
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//! - `price(book, dollars)`: price of each book
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//!
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//! Rule:
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//! - `Q(name, book, dollars) :- author(name, book), bestseller(book), price(book, dollars).`
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//! ("Authors of bestsellers along with each book's price.")
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//!
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//! The plan first scans each input table, then narrows `author` to authors of
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//! bestsellers via a semijoin against `bestseller`, then attaches each book's
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//! price via a natural join against `price`.
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use query_ops::atom::{AtomPattern, Term, scan_atom};
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use query_ops::join::{natural_join, semijoin};
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use query_ops::table::Table;
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use query_ops::value::Value;
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fn s(x: &str) -> Value {
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Value::Str(x.to_string())
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}
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fn i(x: i64) -> Value {
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Value::Int(x)
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}
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#[test]
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fn authors_of_bestsellers_with_price() {
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let author = Table::from_rows(
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2,
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vec![
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vec![s("Alice"), s("Foo")],
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vec![s("Bob"), s("Bar")],
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vec![s("Alice"), s("Baz")],
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vec![s("Carol"), s("Qux")],
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],
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);
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let bestseller = Table::from_rows(1, vec![vec![s("Foo")], vec![s("Baz")]]);
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let price = Table::from_rows(
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2,
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vec![
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vec![s("Foo"), i(25)],
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vec![s("Bar"), i(15)],
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vec![s("Baz"), i(30)],
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vec![s("Qux"), i(20)],
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],
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);
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let author_rel = scan_atom(
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&author,
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&AtomPattern {
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columns: vec![Term::Var("name".to_string()), Term::Var("book".to_string())],
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},
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);
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let bestseller_rel = scan_atom(
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&bestseller,
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&AtomPattern {
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columns: vec![Term::Var("book".to_string())],
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},
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);
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let price_rel = scan_atom(
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&price,
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&AtomPattern {
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columns: vec![
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Term::Var("book".to_string()),
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Term::Var("dollars".to_string()),
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],
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},
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);
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let authors_of_bestsellers = semijoin(&author_rel, &bestseller_rel);
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let result = natural_join(&authors_of_bestsellers, &price_rel);
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assert_eq!(
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result.columns,
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vec![
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"name".to_string(),
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"book".to_string(),
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"dollars".to_string()
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],
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);
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assert_eq!(
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result.rows,
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vec![
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vec![s("Alice"), s("Foo"), i(25)],
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vec![s("Alice"), s("Baz"), i(30)],
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],
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);
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}
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