在開發過程中，突然遇到ORA-02287錯誤 “此處不允許序號”
初始的sql是這樣的
select s_id.nextval, a.name, a.dept, max(b.score)
from tableA a
left join tableB b
on b.user_code = a.code

之前另一個類似的sql沒有使用max（）是可以正常執行的，因此基本定位是max函式導致的這個問題。

網路搜尋發現，oracle的序列有一堆使用限制條件的
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 –這個就是我遇到的那種情況
■ 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

修正後，sql為：
select s_id.nextval, a.name, a.dept, b.score
from tableA a
left join
(
select user_code, max(b.score) score from TableB
group by user_code
)b
on b.user_code = a.code

sql正常執行，並取得預期結果。