docs: private SelectSubqueryExpression parseSubqueryExpression(VoltXMLElement exprNode) {
          assert(exprNode.children.size() == 1);
          VoltXMLElement subqueryElmt = exprNode.children.get(0);
          AbstractParsedStmt subqueryStmt = parseSubquery(subqueryElmt);
          // add table to the query cache
          String withoutAlias = null;
          StmtSubqueryScan stmtSubqueryScan =
                  addSubqueryToStmtCache(subqueryStmt, withoutAlias);
          // Set to the default SELECT_SUBQUERY. May be overridden depending on the context
          return new SelectSubqueryExpression(ExpressionType.SELECT_SUBQUERY, stmtSubqueryScan);
      }