Dwrite commented on code in PR #4692:
URL: https://github.com/apache/calcite/pull/4692#discussion_r2686707455
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core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java:
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@@ -223,6 +223,73 @@ private static class AliasReplacementShuttle extends
SqlShuttle {
}
}
+ /**
+ * Wraps a nested join into a subquery with explicit column aliases.
+ *
+ * <p>This is specifically required for dialects like ClickHouse where the
+ * identifier resolver cannot resolve columns with internal table qualifiers
+ * (e.g., 'd1.loc') when they are wrapped in a subquery alias. By forcing
+ * an explicit 'AS' projection for every column, we ensure the identifiers
+ * are flattened and visible to the outer query block.
+ *
+ * @param input The Result of the nested join branch
+ * @param inputRel The RelNode representing the join branch to extract row
types
+ * @param outerAlias The alias to be assigned to the wrapped subquery
+ * @return A new Result containing the wrapped SQL with explicit aliases
+ */
+ protected Result wrapNestedJoin(Result input, RelNode inputRel, String
outerAlias) {
+ final SqlParserPos pos = SqlParserPos.ZERO;
+
+ // Extract the underlying SqlSelect from the input Result.
+ // We manipulate the Select node directly to avoid redundant nesting
+ // often introduced by Result.asSelect().
+ final SqlSelect innerSelect = input.asSelect();
Review Comment:
I checked the code In RelToSqlConverter, input.asSelect() is designed to
normalize any SqlNode (including SqlCall for VALUES or SetOp) into a SqlSelect
structure.
If the underlying node is not a SELECT, Calcite's SqlImplementor
automatically wraps it in a sub-query. This ensures we always have a SqlSelect
container to safely apply the mandatory aliases required by ClickHouse without
breaking the SQL syntax.
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