关于oracle：pl/sql中的嵌套PIPELINED函数

Nested PIPELINED function in pl/sql

我必须在 pl/sql 中编写一个嵌套的流水线函数，我尝试通过以下方式实现它。

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CREATE PACKAGE BODY XYZ AS
FUNCTION main_xyz RETURN data_type_1 pipelined IS
BEGIN
--code
pipe ROW(sub_func);
END;
FUNCTION sub_func RETURN data_type_1 pipelined IS
BEGIN
--code
pipe ROW(sub_func_1);
END;
FUNCTION sub_func_1 RETURN data_type_1 pipelined IS
BEGIN
--code
pipe ROW(main_abc);
END;
END;

CREATE PACKAGE BODY abc AS
FUNCTION main_abc RETURN data_type_2 pipelined IS
var data_type_2;
BEGIN
--code
RETURN var;
END;
END;

但是，我收到以下错误

[Error] PLS-00653 : PLS-00653: aggregate/table functions are not
allowed in PL/SQL scope

我哪里错了？是语法还是逻辑？