[GitHub] [spark] aokolnychyi commented on a change in pull request #31580: [SPARK-34457][SQL] DataSource V2: Add default null ordering to SortDirection

[GitBox <gi...@apache.org>]

aokolnychyi commented on a change in pull request #31580:
URL: https://github.com/apache/spark/pull/31580#discussion_r585244508



##########
File path: sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions/SortDirection.java
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@@ -19,14 +19,33 @@
 
 import org.apache.spark.annotation.Experimental;
 
+import static org.apache.spark.sql.connector.expressions.NullOrdering.NULLS_FIRST;
+import static org.apache.spark.sql.connector.expressions.NullOrdering.NULLS_LAST;
+
 /**
  * A sort direction used in sorting expressions.
+ * <p>
+ * Each direction has a default null ordering that is implied if no null ordering is specified
+ * explicitly.
  *
  * @since 3.2.0
  */
 @Experimental
 public enum SortDirection {
-  ASCENDING, DESCENDING;
+  ASCENDING(NULLS_FIRST), DESCENDING(NULLS_LAST);
+
+  private final NullOrdering defaultNullOrdering;
+
+  SortDirection(NullOrdering defaultNullOrdering) {
+    this.defaultNullOrdering = defaultNullOrdering;
+  }
+
+  /**
+   * Returns the default null ordering to use if no null ordering is specified explicitly.
+   */
+  public NullOrdering defaultNullOrdering() {

Review comment:
       If we decide to introduce this, I think it makes sense to leverage it in `Expressions$sort` as @cloud-fan said. That's a good use case.
   
   @HeartSaVioR, could you give an example, please? I am not sure I fully got it. Do you mean to make `nullOrdering` in `SortOrder` optional instead of exposing a default null ordering in `SortDirection`? If so, I usually prefer to use the simplest types in the API. Using `Optional` will make the API harder to use, in my view. In addition, we probably want to handle `SortDirection` in the same way as it is also optional.




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