[GitHub] [spark] maropu commented on a change in pull request #27965: [SPARK-31205][SQL] support string literal as the second argument of date_add/date_sub functions

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maropu commented on a change in pull request #27965: [SPARK-31205][SQL] support string literal as the second argument of date_add/date_sub functions
URL: https://github.com/apache/spark/pull/27965#discussion_r395585654
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala
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 @@ -1043,6 +1044,22 @@ object TypeCoercion {
       }
     }
   }
+
+  /**
+   * A special rule to support string literal as the second argument of date_add/date_sub functions,
+   * to keep backward compatibility.
+   * TODO: revisit the type coercion rules for string.
+   */
+  object StringLiteralCoercion extends TypeCoercionRule {
+    override protected def coerceTypes(plan: LogicalPlan): LogicalPlan = plan resolveExpressions {
+      // Skip nodes who's children have not been resolved yet.
+      case e if !e.childrenResolved => e
+      case DateAdd(l, r) if r.dataType == StringType && r.foldable =>
+        DateAdd(l, AnsiCast(r, IntegerType))
 
 Review comment:
   Ah, yes. I rechecked the references of implicit casts in some databases, as you said, the cast seems to be acceptable.

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