[GitHub] [spark] amaliujia commented on a diff in pull request #38973: [WIP][SPARK-41439][CONNECT][PYTHON] Implement `DataFrame.melt`

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

amaliujia commented on code in PR #38973:
URL: https://github.com/apache/spark/pull/38973#discussion_r1042904146


##########
connector/connect/common/src/main/protobuf/spark/connect/relations.proto:
##########
@@ -570,3 +571,21 @@ message Hint {
   // (Optional) Hint parameters.
   repeated Expression.Literal parameters = 3;
 }
+
+// Unpivot a DataFrame from wide format to long format, optionally leaving identifier columns set.
+message Melt {
+  // (Required) The input relation.
+  Relation input = 1;
+
+  // (Required) Id columns.
+  repeated Expression ids = 2;

Review Comment:
   Yes Expression is right. Honestly I think Expression is used more often than `Column` for relational world



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