SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Function mapAdd (children 1)
     ExpressionList (children 2)
      Function map (children 1)
       ExpressionList (children 4)
        Function CAST (children 1)
         ExpressionList (children 2)
          Literal \'a\'
          Literal \'LowCardinality(String)\'
        Literal UInt64_1
        Literal \'b\'
        Literal UInt64_1
      Function map (children 1)
       ExpressionList (children 2)
        Identifier key
        Literal UInt64_1
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      Function values (children 1)
       ExpressionList (children 4)
        Literal \'key String\'
        Literal \'b\'
        Literal \'c\'
        Literal \'d\'
