Oracle中Dual的使用

以下是dual的一些使用方法：

查看当前连接用户

SQL> select user from dual;

USER
------------------------------
SYSTEM

查看当前日期、时间

SQL> select sysdate from dual;

SYSDATE
----------
18-3月 -01

SQL> select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;

TO_CHAR(SYSDATE,'YY
-------------------
2001-03-18 22:37:56

当作计算器用

SQL> select 1+2 from dual;

1+2
----------
3
查看序列值

SQL> create sequence aaa increment by 1 start with 1;
SQL> select aaa.nextval from dual;

SQL> select aaa.nextval from dual;

NEXTVAL
----------
1

SQL> select aaa.currval from dual;

CURRVAL
----------
1