开发人员反映序列不能使用，自己回来测试了一下

select test.sequence.nextval,mgr,sum(sal) from emp group by mgr
 
ORA-02287: 此处不允许序号

果然，在外面再包一层就可以了

SQL> select test_sequence.nextval,mgr,sm from (select mgr,sum(sal) sm from emp group by mgr );
 
   NEXTVAL   MGR         SM
---------- ----- ----------
        27  7839       8275
        28  7782       1300
        29  7698       6550
        30  7902       5800
        31  7566       6000
        32  7788       1100
 
6 rows selected

看来序列使用时有限制的

看到书上说有这么多限制

Restrictions on Sequence Values You cannot use CURRVAL and NEXTVAL in the
following constructs:
■ A subquery in a DELETE, SELECT, or UPDATE statement
■ A query of a view or of a materialized view
■ A SELECT statement with the DISTINCT operator
■ A SELECT statement with a GROUP BY clause or ORDER BY clause    --这个就是我遇到的那种情况
■ A SELECT statement that is combined with another SELECT statement with the
UNION, INTERSECT, or MINUS set operator
■ The WHERE clause of a SELECT statement
■ The DEFAULT value of a column in a CREATE TABLE or ALTER TABLE statement
■ The condition of a CHECK constrain

总结，无法使用序列的CURRVAL 和NEXTVAL的情况为：

■ A subquery in a DELETE, SELECT, or UPDATE statement

（子查询包括在DELETE,SELECT,UPDATE语句中）
■ A query of a view or of a materialized view

（对视图和物化视图的查询）
■ A SELECT statement with the DISTINCT operator

（SELECT查询中用到了DISTINCT）
■ A SELECT statement with a GROUP BY clause or ORDER BY clause    --这个就是我遇到的那种情况

（SELECT查询中用到了GROUP BY ,ORDER BY )
■ A SELECT statement that is combined with another SELECT statement with the
UNION, INTERSECT, or MINUS set operator

(SELECT查询和其他SELECT查询结合，并且用到了UNION,INTERSECT,MINUS等操作）
■ The WHERE clause of a SELECT statement

（SELECT查询语句中的where条件不能用序列

例子：select 1 from dual where t_emp_calendar_seq.nextval = 95）
■ The DEFAULT value of a column in a CREATE TABLE or ALTER TABLE statement

（？？）
■ The condition of a CHECK constrain

（在CHECK限制条件中不能用）