[GitHub] [spark] gengliangwang commented on a diff in pull request #36960: [SPARK-39557][SQL] Support ARRAY, STRUCT, MAP types as DEFAULT values

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

gengliangwang commented on code in PR #36960:
URL: https://github.com/apache/spark/pull/36960#discussion_r911475487


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/ResolveDefaultColumnsUtil.scala:
##########
@@ -120,6 +120,54 @@ object ResolveDefaultColumns {
     }
   }
 
+  /**
+   * Computes the string representation of an expression suitable for use when storing the
+   * constant-folded result of DEFAULT column values.
+   */
+  private def expressionToString(expression: Expression): String = {
+    expression match {
+      case Cast(child, dataType, _, _) =>
+        s"CAST(${expressionToString(child)} AS ${dataType.catalogString})"
+      case Literal(value, dataType: DataType) =>
+        valueToString(value, dataType)
+      case _ =>
+        expression.sql
+    }
+  }
+
+  /**
+   * Computes the string representation of a value suitable for use when storing the
+   * constant-folded result of DEFAULT column values.
+   */
+  private def valueToString(value: Any, dataType: DataType): String = {
+    (value, dataType) match {
+      case (data: GenericArrayData, arrayType: ArrayType) =>

Review Comment:
   Shall we fix the `sql` method of `Literal` instead?



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