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[PyLimit] adding skip and fetch with datafusion expr support #1674

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[PyLimit] adding skip and fetch with datafusion expr support #1674

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29 changes: 17 additions & 12 deletions crates/core/src/expr/limit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@ use pyo3::IntoPyObjectExt;
use pyo3::prelude::*;

use crate::common::df_schema::PyDFSchema;
use crate::expr::PyExpr;
use crate::expr::logical_node::LogicalNode;
use crate::sql::logical::PyLogicalPlan;

Expand Down Expand Up @@ -64,19 +65,23 @@ impl Display for PyLimit {

#[pymethods]
impl PyLimit {
// NOTE: Upstream now has expressions for skip and fetch
// TODO: Do we still want to expose these?
// REF: https://github.com/apache/datafusion/pull/12836

// /// Retrieves the skip value for this `Limit`
// fn skip(&self) -> usize {
// self.limit.skip
// }
// Retrieves the skip expression for this `Limit`, if any.
//
// `LIMIT`/`OFFSET` were changed upstream to support arbitrary
// expressions (not just constants), see
// https://github.com/apache/datafusion/pull/13028. Callers that expect
// a simple literal (the common case, e.g. `OFFSET 5`) should evaluate
// the returned `PyExpr` via `Expr.python_value()`.
fn skip(&self) -> PyResult<Option<PyExpr>> {
Ok(self.limit.skip.as_deref().cloned().map(PyExpr::from))
}

// /// Retrieves the fetch value for this `Limit`
// fn fetch(&self) -> Option<usize> {
// self.limit.fetch
// }
// Retrieves the fetch expression for this `Limit`, if any.
//
// See the note on `skip` above regarding expression-based limits.
fn fetch(&self) -> PyResult<Option<PyExpr>> {
Ok(self.limit.fetch.as_deref().cloned().map(PyExpr::from))
}

/// Retrieves the input `LogicalPlan` to this `Limit` node
fn input(&self) -> PyResult<Vec<PyLogicalPlan>> {
Expand Down
4 changes: 4 additions & 0 deletions python/tests/test_expr.py
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Expand Up @@ -115,13 +115,17 @@ def test_limit(test_ctx):
plan = plan.to_variant()
assert isinstance(plan, Limit)
assert "Skip: None" in str(plan)
assert plan.skip() is None
assert plan.fetch().python_value().as_py() == 10

df = test_ctx.sql("select c1 from test LIMIT 10 OFFSET 5")
plan = df.logical_plan()

plan = plan.to_variant()
assert isinstance(plan, Limit)
assert "Skip: Some(Literal(Int64(5), None))" in str(plan)
assert plan.skip().python_value().as_py() == 5
assert plan.fetch().python_value().as_py() == 10


def test_aggregate_query(test_ctx):
Expand Down
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