Github user wuchong commented on a diff in the pull request:
https://github.com/apache/flink/pull/4274#discussion_r127382075
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/expressions/stringExpressions.scala
---
@@ -277,3 +278,47 @@ case class Overlay(
position.toRexNode)
}
}
+
+/**
+ * Returns the string that results from concatenating the arguments.
+ * Returns NULL if any argument is NULL.
+ */
+case class Concat(strings: Seq[Expression]) extends Expression with
InputTypeSpec {
+
+ override private[flink] def children: Seq[Expression] = strings
+
+ override private[flink] def resultType: TypeInformation[_] =
BasicTypeInfo.STRING_TYPE_INFO
+
+ override private[flink] def expectedTypes: Seq[TypeInformation[_]] =
+ children.map(_ => STRING_TYPE_INFO)
+
+ override def toString: String = s"concat($strings)"
+
+ override private[flink] def toRexNode(implicit relBuilder: RelBuilder):
RexNode = {
+ relBuilder.call(ScalarSqlFunctions.CONCAT, children.map(_.toRexNode))
+ }
+}
+
+/**
+ * Returns the string that results from concatenating the arguments and
separator.
+ * Returns NULL If the separator is NULL.
+ *
+ * Note: this user-defined function does not skip empty strings. However,
it does skip any NULL
+ * values after the separator argument.
+ **/
+case class ConcatWs(separator: Expression, strings: Seq[Expression])
--- End diff --
What about make this signature to `args: Seq[Expression]`, which combines
`separator` and `strings` before construct `ConcatWs`. So that we do not need
to change the FunctionCatalog. I think it's fine, because `ConcatWs` is not
used by users.
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