[GitHub] walterddr commented on a change in pull request #6473: [FLINK-9999] [table] Add ISNUMERIC supported in Table API/SQL

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walterddr commented on a change in pull request #6473: [FLINK-9999] [table] Add ISNUMERIC supported in Table API/SQL
URL: https://github.com/apache/flink/pull/6473#discussion_r209430879
 
 

 ##########
 File path: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/expressions/stringExpressions.scala
 ##########
 @@ -358,6 +358,29 @@ case class Rpad(text: Expression, len: Expression, pad: Expression)
   }
 }
 
+case class IsNumeric(child: Expression) extends UnaryExpression with InputTypeSpec {
+
+  override private[flink] def expectedTypes: Seq[TypeInformation[_]] = Seq(STRING_TYPE_INFO)
+
+  override private[flink] def resultType: TypeInformation[_] = INT_TYPE_INFO
+
+  override private[flink] def validateInput(): ValidationResult = {
+    if (child.resultType == STRING_TYPE_INFO) {
 
 Review comment:
   Wasn't sure if there is a SQL standard for `isNumeric` but some SQL servers such as MS and Transact do support `isNumeric(expression)` where expression can actually be a Numeric type (INT, BIGINT, DOUBLE, etc). Maybe @twalthr have more context ?

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