dssysolyatin commented on code in PR #4692:
URL: https://github.com/apache/calcite/pull/4692#discussion_r2637183810
##########
core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java:
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@@ -223,6 +224,69 @@ private static class AliasReplacementShuttle extends
SqlShuttle {
}
}
+ /**
+ * Wraps a nested join Result into a subquery with a new alias.
+ * Required for dialects like ClickHouse that don't support nested JOIN
syntax.
+ *
+ * @param input the Result from the nested join subtree
+ * @param outerAlias the alias to assign to the wrapped subquery
+ * @return a new Result with the wrapped SQL node
+ */
+ protected Result wrapNestedJoin(Result input, RelNode inputRel, String
outerAlias) {
+ // Get the original SQL node from the input Result
+ final SqlNode original = input.asSelect();
+ // Generate inner alias (different from outer)
+ String innerAlias = "t" + inputRel.getId();
+ // Wrap: original → (SELECT * FROM (original) AS newAlias)
+ SqlNode wrapped = wrapAsSelectStar(original, innerAlias);
+
+ Map<String, RelDataType> newAliases = new LinkedHashMap<>();
+
+ // Add the outer alias with the correct row type
+ newAliases.put(outerAlias, inputRel.getRowType());
+
+ return new Result(
+ wrapped,
+ input.clauses,
+ outerAlias,
+ null,
+ newAliases);
+ }
+
+ /**
+ * Wraps a subquery into a SELECT * FROM (subQuery) AS alias structure.
+ *
+ * @param subQuery the original SQL node to wrap
+ * @param alias the alias to assign to the wrapped subquery
+ * @return a SqlSelect node representing: SELECT * FROM (subQuery) AS alias
+ */
+ protected SqlNode wrapAsSelectStar(SqlNode subQuery, String alias) {
Review Comment:
Can you use `SqlImplementor.wrapSelect` ?
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