(datafusion) 01/01: doc: more comments to `evaluate_selection` function (#24485)

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github-merge-queue[bot] pushed a commit to branch gh-readonly-queue/main/pr-24485-5c1211439efd3d58b9fa39f27ac1d3b18c603b33
in repository https://gitbox.apache.org/repos/asf/datafusion.git

commit 47e47656eb4bb2f74ccf4504263657ebb3dda6fe
Author: Yongting You <20...@gmail.com>
AuthorDate: Thu Aug 20 00:44:26 2026 +0000

    doc: more comments to `evaluate_selection` function (#24485)
    
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---
 .../physical-expr-common/src/physical_expr.rs      | 24 +++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/datafusion/physical-expr-common/src/physical_expr.rs b/datafusion/physical-expr-common/src/physical_expr.rs
index 59393e7578..6be291881e 100644
--- a/datafusion/physical-expr-common/src/physical_expr.rs
+++ b/datafusion/physical-expr-common/src/physical_expr.rs
@@ -93,12 +93,30 @@ pub trait PhysicalExpr: Any + Send + Sync + Display + Debug + DynEq + DynHash {
             self.nullable(input_schema)?,
         )))
     }
-    /// Evaluate an expression against a RecordBatch after first applying a validity array
+    /// Evaluates this expression only for rows where `selection` is `true`.
+    ///
+    /// Rows where `selection` is `false` or null are skipped during evaluation and
+    /// produce `NULL` in the result. Thus, values in those rows cannot trigger
+    /// evaluation errors such as division by zero.
+    ///
+    /// # Example
+    ///
+    /// Given `expr = 4 / val`:
+    ///
+    /// ```text
+    /// val  selection | result
+    ///   0      false |   NULL
+    ///   1       true |      4
+    ///   2       true |      2
+    /// ```
+    ///
+    /// The first row is not evaluated, avoiding division by zero. Its result is
+    /// `NULL`.
     ///
     /// # Errors
     ///
-    /// Returns an `Err` if the expression could not be evaluated or if the length of the
-    /// `selection` validity array and the number of row in `batch` is not equal.
+    /// Returns an `Err` if the expression could not be evaluated or if the length of
+    /// `selection` does not equal the number of rows in `batch`.
     fn evaluate_selection(
         &self,
         batch: &RecordBatch,


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