#字段(field)基本上和列(column)的意思相同

SELECT Concat(vend_name, ' (', vend_country, ')') FROM vendors

ORDER BY vend_name; #多数DBMS使用+或||来实现拼接，MySQL则使用Concat()函数来实现。

SELECT Concat(RTrim(vend_name), ' (', RTrim(vend_country), ')') FROM vendors

ORDER BY vend_name; #RTrim()去掉值右边所有的空格，LTrim()和Trim()则分别表示去掉左边和左右两边的所有空格

SELECT Concat(RTrim(vend_name), ' (', RTrim(vend_country), ')') AS vend_titile FROM vendors

ORDER BY vend_name;

SELECT prod_id, quantity, item_price, quantity*item_price AS expanded_price From orderitems

WHERE order_num = 20005;

SELECT 3*2;

SELECT Trim(' abc ');

SELECT Now(); #用于测试计算结果