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query.rs
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query.rs
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use super::QueryIterator;
use crate::errinput;
use crate::error::Result;
use crate::sql::plan::Direction;
use crate::sql::types::{Column, Expression, Row, Value};
/// A filter executor
pub struct Filter {
source: QueryIterator,
predicate: Expression,
}
impl Filter {
pub fn new(source: QueryIterator, predicate: Expression) -> Self {
Self { source, predicate }
}
pub fn execute(self) -> QueryIterator {
QueryIterator {
columns: self.source.columns,
rows: Box::new(self.source.rows.filter_map(move |r| {
r.and_then(|row| match self.predicate.evaluate(Some(&row))? {
Value::Boolean(true) => Ok(Some(row)),
Value::Boolean(false) => Ok(None),
Value::Null => Ok(None),
value => errinput!("filter returned {value}, expected boolean",),
})
.transpose()
})),
}
}
}
/// A projection executor
pub struct Projection {
source: QueryIterator,
expressions: Vec<(Expression, Option<String>)>,
}
impl Projection {
pub fn new(source: QueryIterator, expressions: Vec<(Expression, Option<String>)>) -> Self {
Self { source, expressions }
}
pub fn execute(self) -> QueryIterator {
let (expressions, labels): (Vec<Expression>, Vec<Option<String>>) =
self.expressions.into_iter().unzip();
let columns = expressions
.iter()
.enumerate()
.map(|(i, e)| {
if let Some(Some(label)) = labels.get(i) {
Column { name: Some(label.clone()) }
} else if let Expression::Field(i, _) = e {
self.source.columns.get(*i).cloned().unwrap_or(Column { name: None })
} else {
Column { name: None }
}
})
.collect();
let rows = Box::new(self.source.rows.map(move |r| {
r.and_then(|row| {
expressions.iter().map(|e| e.evaluate(Some(&row))).collect::<Result<_>>()
})
}));
QueryIterator { columns, rows }
}
}
/// An ORDER BY executor
pub struct Order {
source: QueryIterator,
order: Vec<(Expression, Direction)>,
}
impl Order {
pub fn new(source: QueryIterator, order: Vec<(Expression, Direction)>) -> Self {
Self { source, order }
}
pub fn execute(mut self) -> Result<QueryIterator> {
// FIXME Since we can't return errors from the sort_by closure, we have
// to pre-evaluate all values. This means that we can't short-circuit
// evaluation, and have to temporarily store evaluated values, which is
// bad for performance and memory usage respectively
struct Item {
row: Row,
values: Vec<Value>,
}
let mut items = Vec::new();
while let Some(row) = self.source.next().transpose()? {
let mut values = Vec::new();
for (expr, _) in self.order.iter() {
values.push(expr.evaluate(Some(&row))?);
}
items.push(Item { row, values })
}
let order = &self.order;
items.sort_by(|a, b| {
for (i, (_, order)) in order.iter().enumerate() {
let value_a = &a.values[i];
let value_b = &b.values[i];
match value_a.partial_cmp(value_b) {
Some(std::cmp::Ordering::Equal) => {}
Some(o) => return if *order == Direction::Ascending { o } else { o.reverse() },
None => {}
}
}
std::cmp::Ordering::Equal
});
Ok(QueryIterator {
columns: self.source.columns,
rows: Box::new(items.into_iter().map(|i| Ok(i.row))),
})
}
}
/// A LIMIT executor
pub struct Limit {
source: QueryIterator,
limit: u64,
}
impl Limit {
pub fn new(source: QueryIterator, limit: u64) -> Self {
Self { source, limit }
}
pub fn execute(self) -> QueryIterator {
QueryIterator {
columns: self.source.columns,
rows: Box::new(self.source.rows.take(self.limit as usize)),
}
}
}
/// An OFFSET executor
pub struct Offset {
source: QueryIterator,
offset: u64,
}
impl Offset {
pub fn new(source: QueryIterator, offset: u64) -> Self {
Self { source, offset }
}
pub fn execute(self) -> QueryIterator {
QueryIterator {
columns: self.source.columns,
rows: Box::new(self.source.rows.skip(self.offset as usize)),
}
}
}