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src/Interpreters/ActionsDAG.h

@@ -507,6 +507,9 @@ struct ActionDAGNodes
     ActionsDAG::NodeRawConstPtrs nodes;
 };
 
+/// Helper for query analysis.
+/// If project_input is set, all columns not found in inputs should be removed.
+/// Now, we do it before adding a step to query plan by calling appendInputsForUnusedColumns.
 struct ActionsAndProjectInputsFlag
 {
     ActionsDAG dag;