xuzifu666 commented on code in PR #5253:
URL: https://github.com/apache/calcite/pull/5253#discussion_r3968999463
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core/src/main/java/org/apache/calcite/sql2rel/RelFieldTrimmer.java:
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@@ -1303,6 +1308,11 @@ public TrimResult trimFields(
// because zero-column records are illegal. Give them the last field,
// which is unlikely to be a system field.
if (fieldsUsed.isEmpty()) {
+ if (fieldCount == 0) {
Review Comment:
You're right that it looks contradictory. I've reworded the comment to
explain the edge case: the "keep the last field" rule only applies when there
is a last field. If the input already has zero columns, we can't manufacture
one, so we return it unchanged. This matches the fix for SetOp as well.
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