sql - 枢轴查询给出列定义不明确的错误

Question

对于这个查询

select * from(select occupation from occupations)
    pivot xml(
        count(occupation) 
        for occupation in (select distinct occupation from occupations));

我收到错误 ORA-00918: column ambiguously defined。

这个表：

    Ashley Professor

    Samantha Actor

    Julia Doctor

    Britney Professor

    Maria Professor

    Meera Professor

    Priya Doctor

    Priyanka Professor

    Jennifer Actor

    Ketty Actor

    Belvet Professor

    Naomi Professor

    Jane Singer

    Jenny Singer

    Kristeen Singer

    Christeen Singer

    Eve Actor

    Aamina Doctor

关于导致此错误的任何线索。虽然结果不构成任何有意义的数据，但需要知道导致此错误的原因。

有了这个查询，一切都很好：

select * from(
    select name,occupation from occupations)
    pivot (
        count(occupation) 
        for occupation in ('Doctor','Actor','Singer','Professor'));

这两者有什么区别？