SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function if (children 1)
     ExpressionList (children 3)
      Function materialize (children 1)
       ExpressionList (children 1)
        Literal UInt64_0
      Function materialize (children 1)
       ExpressionList (children 1)
        Function toLowCardinality (children 1)
         ExpressionList (children 1)
          Literal \'a\'
      Function materialize (children 1)
       ExpressionList (children 1)
        Literal \'b\'
