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

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

cloud-fan commented on a change in pull request #31580:
URL: https://github.com/apache/spark/pull/31580#discussion_r585660456



##########
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:
       @HeartSaVioR `SortOrder` is not an API we ask users to implement. The users should call `Expressions.sort` to create an instance of `SortOrder`.
   
   That's why I suggested adding an overload of `Expressions.sort`, as that makes null ordering optional to the users.




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