查询oracle数据库的隔离级别

oracle数据库似乎必须要在某个事物里，才能查询隔离级别：
-- 让当前session处于一个事物中
declare
trans_id Varchar2(100);
begin
trans_id := dbms_transaction.local_transaction_id( TRUE );
end;
-- 查询隔离级别
SELECT s.sid, s.serial#,
CASE BITAND(t.flag, POWER(2, 28))
WHEN 0 THEN 'READ COMMITTED'
ELSE 'SERIALIZABLE'
END AS isolation_level
FROM vsession s ON t.addr = s.taddr AND s.sid = sys_context('USERENV', 'SID');

参考文献
[1] https://blog.csdn.net/nanxiaotao/article/details/80412196