SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Function mapFromArrays (children 1)
     ExpressionList (children 2)
      Function array (children 1)
       ExpressionList (children 2)
        Function toLowCardinality (children 1)
         ExpressionList (children 1)
          Function toNullable (children 1)
           ExpressionList (children 1)
            Literal \'a\'
        Function toLowCardinality (children 1)
         ExpressionList (children 1)
          Function toNullable (children 1)
           ExpressionList (children 1)
            Literal \'b\'
      Literal Array_[UInt64_1, UInt64_2]
   ExpressionList (children 1)
    Literal UInt64_1
