[GitHub] [orc] stiga-huang commented on a change in pull request #1024: ORC-1099: [C++] Extend ReadIntent to support MAP and UNION type

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

stiga-huang commented on a change in pull request #1024:
URL: https://github.com/apache/orc/pull/1024#discussion_r796459654



##########
File path: c++/src/Reader.cc
##########
@@ -120,10 +120,24 @@ namespace orc {
   bool ColumnSelector::selectParents(std::vector<bool>& selectedColumns, const Type& type) {
     size_t id = static_cast<size_t>(type.getColumnId());
     bool result = selectedColumns[id];
+    uint64_t numSubtypeSelected = 0;
     for(uint64_t c=0; c < type.getSubtypeCount(); ++c) {
-      result |= selectParents(selectedColumns, *type.getSubtype(c));
+      if (selectParents(selectedColumns, *type.getSubtype(c))) {
+        result = true;
+        numSubtypeSelected++;
+      }
     }
     selectedColumns[id] = result;
+
+    if (type.getKind() == TypeKind::UNION && selectedColumns[id]) {
+      if (0 < numSubtypeSelected && numSubtypeSelected < type.getSubtypeCount()) {
+        // Subtypes of UNION should be fully selected or not selected at all.
+        // Override partial subtype selections with full selections.
+        for (uint64_t c = 0; c < type.getSubtypeCount(); ++c) {

Review comment:
       Ah, right. Thanks for the explanation!




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