SQL UNION 与 UNION ALL用法
直接上例子
例子中用到的两张表:
Employees_China:
E_ID | E_Name |
---|---|
01 | Zhang, Hua |
02 | Wang, Wei |
03 | Carter, Thomas |
04 | Yang, Ming |
Employees_USA:
E_ID | E_Name |
---|---|
01 | Adams, John |
02 | Bush, George |
03 | Carter, Thomas |
04 | Gates, Bill |
使用 UNION 命令(类似数学中的并集)
SELECT E_Name FROM Employees_ChinaUNION
SELECT E_Name FROM Employees_USA
结果
E_Name |
---|
Zhang, Hua |
Wang, Wei |
Carter, Thomas |
Yang, Ming |
Adams, John |
Bush, George |
Gates, Bill |
使用 UNION ALL 命令
SELECT E_Name FROM Employees_ChinaUNION ALL
SELECT E_Name FROM Employees_USA
E_Name |
---|
Zhang, Hua |
Wang, Wei |
Carter, Thomas |
Yang, Ming |
Adams, John |
Bush, George |
Carter, Thomas |
Gates, Bill |