[GitHub] [spark] gengliangwang commented on a change in pull request #25239: [WIP][SPARK-28495][SQL] Table insertion: follow store assignment rules of ANSI SQL

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

gengliangwang commented on a change in pull request #25239: [WIP][SPARK-28495][SQL] Table insertion: follow store assignment rules of ANSI SQL
URL: https://github.com/apache/spark/pull/25239#discussion_r306791840
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
 ##########
 @@ -2665,6 +2666,38 @@ class Analyzer(
       }
     }
   }
+
+  /**
+   * Replace the [[AssignableCast]] expression by [[Cast]], and throw exceptions if the cast is
+   * not assignable.
+   */
+  object ResolveAssignableCast extends Rule[LogicalPlan] {
+    private def fail(from: Expression, to: DataType, walkedTypePath: Seq[String]) = {
+      val fromStr = from match {
+        case l: LambdaVariable => "array element"
+        case e => e.sql
+      }
+      throw new AnalysisException(s"Cannot assign $fromStr from " +
+        s"${from.dataType.catalogString} to ${to.catalogString}.\n" +
+        "The type path of the target object is:\n" + walkedTypePath.mkString("", "\n", "\n") +
+        "You can add an explicit cast to the input data.")
+    }
+
+    def apply(plan: LogicalPlan): LogicalPlan = plan.resolveOperatorsUp {
+      case p if !p.childrenResolved => p
+      case p if p.resolved => p
+
+      case p => p transformExpressions {
+        case u @ AssignableCast(child, _, _) if !child.resolved => u
+
+        case AssignableCast(child, dataType, walkedTypePath)
+          if !Cast.canAssign(child.dataType, dataType) =>
+          fail(child, dataType, walkedTypePath)
+
+        case AssignableCast(child, dataType, _) => Cast(child, dataType.asNullable)
 
 Review comment:
   @maropu nice catch. It seems that it is an existing issue in Cast. We can fix it first.

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