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)
        Function toLowCardinality (children 1)
         ExpressionList (children 1)
          Literal \'b\'
