[Tips]如何在CentOS 7切換Linux runlevel?

新的CentOS7採用了systemctl來取代很多舊有的指令，現在我們也要使用這個來進行runlevel(target)的切換。

1)切換到純文字介面(類似以前的runlevel3)
[root@centOS7 ~]# systemctl isolate multi-user.target

2)切換到圖形化介面(類似以前的runlevel5)
[root@centOS7 ~]# systemctl isolate graphical.target

3)顯示目前預設target
[root@centOS7 ~]# systemctl get-default
multi-user.target

4)變更預設target
[root@centOS7 ~]# systemctl set-default graphical.target

SQL語法_Select

話說前陣子才剛通過了Oracle Database 11g: SQL Fundamentals I，趁記憶猶新的時候趕快來整理一下Oracle的SQL語法吧。

---

SELECT   *│{[DISTINCT column│expression [alias],‧‧‧}
FROM       table;

---

• SELECT    *
  FROM       departments;

DEPARTMENT_ID	DEPARTMENT_NAME	LOCATION_ID
10	Marketing	170
20	Administration	180
50	IT	150
80	Sales	170

• SELECT    department_id, department_name FROM       departments;

DEPARTMENT_ID	DEPARTMENT_NAME
10	Marketing
20	Administration
50	IT
80	Sales

• SELECT    department_name, salary, salary + 500FROM       departments;

DEPARTMENT_NAME	SALARY	SALARY + 500
Marketing	200	700
Administration	500	1000
IT	300	800
Sales	400	900