联合 ALL

UNION ALL 从客户和供应商表中选择所有（重复值）城市。

查询：

SELECT City FROM Customers
UNION ALL
SELECT City FROM Suppliers
ORDER BY City;

结果：

Number of Records: 12

CityAachen
Albuquerque
Anchorage
Ann Arbor
Annecy
Barcelona
Barquisimeto
Bend
Bergamo
Berlin
Berlin
Bern