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use crate::TransformArgs;
use mz_expr::visit::Visit;
use mz_expr::MirRelationExpr;
#[derive(Debug)]
pub struct TopKElision;
impl crate::Transform for TopKElision {
#[tracing::instrument(
target = "optimizer"
level = "trace",
skip_all,
fields(path.segment = "topk_elision")
)]
fn transform(
&self,
relation: &mut MirRelationExpr,
_: TransformArgs,
) -> Result<(), crate::TransformError> {
let result = relation.try_visit_mut_post(&mut |e| self.action(e));
mz_repr::explain::trace_plan(&*relation);
result
}
}
impl TopKElision {
pub fn action(&self, relation: &mut MirRelationExpr) -> Result<(), crate::TransformError> {
if let MirRelationExpr::TopK {
input,
group_key: _,
order_key: _,
limit,
offset,
monotonic: _,
} = relation
{
if limit.is_none() && *offset == 0 {
*relation = input.take_dangerous();
} else if limit == &Some(0) {
relation.take_safely();
}
}
Ok(())
}
}