ozankabak commented on code in PR #16217:
URL: https://github.com/apache/datafusion/pull/16217#discussion_r2126840903
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datafusion/physical-expr/src/equivalence/ordering.rs:
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@@ -16,115 +16,76 @@
// under the License.
use std::fmt::Display;
-use std::hash::Hash;
+use std::ops::Deref;
use std::sync::Arc;
use std::vec::IntoIter;
-use crate::equivalence::add_offset_to_expr;
-use crate::{LexOrdering, PhysicalExpr};
+use crate::expressions::with_new_schema;
+use crate::{add_offset_to_physical_sort_exprs, LexOrdering, PhysicalExpr};
use arrow::compute::SortOptions;
-use datafusion_common::HashSet;
+use arrow::datatypes::SchemaRef;
+use datafusion_common::{HashSet, Result};
+use datafusion_physical_expr_common::sort_expr::PhysicalSortExpr;
-/// An `OrderingEquivalenceClass` object keeps track of different alternative
-/// orderings than can describe a schema. For example, consider the following
table:
+/// An `OrderingEquivalenceClass` keeps track of distinct alternative orderings
+/// than can describe a table. For example, consider the following table:
///
/// ```text
-/// |a|b|c|d|
-/// |1|4|3|1|
-/// |2|3|3|2|
-/// |3|1|2|2|
-/// |3|2|1|3|
+/// ┌───┬───┬───┬───┐
+/// │ a │ b │ c │ d │
+/// ├───┼───┼───┼───┤
+/// │ 1 │ 4 │ 3 │ 1 │
+/// │ 2 │ 3 │ 3 │ 2 │
+/// │ 3 │ 1 │ 2 │ 2 │
+/// │ 3 │ 2 │ 1 │ 3 │
+/// └───┴───┴───┴───┘
/// ```
///
-/// Here, both `vec![a ASC, b ASC]` and `vec![c DESC, d ASC]` describe the
table
+/// Here, both `[a ASC, b ASC]` and `[c DESC, d ASC]` describe the table
/// ordering. In this case, we say that these orderings are equivalent.
Review Comment:
An ordering equivalence class is basically a set of orderings, and if the
table in question has no orderings, the set will be empty (which is a
common/valid case). I will add some comments clarifying this.
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