DescribeQuery (children 1)
 TableExpression (children 1)
  Subquery (children 1)
   SelectWithUnionQuery (children 1)
    ExpressionList (children 1)
     SelectQuery (children 1)
      ExpressionList (children 3)
       Subquery (alias c) (children 1)
        SelectWithUnionQuery (children 1)
         ExpressionList (children 1)
          SelectQuery (children 1)
           ExpressionList (children 2)
            Literal UInt64_1 (alias a)
            Literal UInt64_2 (alias b)
       Identifier c.a
       Identifier c.b