拼接两个列，使用concat()函数来实现

select concat(id,name)
from student
order by id;

输出结果为：
concat(id,name)

1luzhaoshan
2liumeidi
3luxinyan
4luchuanhang

使用别名as

select concat(id,name) as student_title
from student
order by id;

输出结果为：
 student_title

1luzhaoshan
2liumeidi
3luxinyan
4luchuanhang

select id,item_price,
id*item_price as money
from orderitems
where id = 1;

查找的结果是：
id    |    item_price    |    money

1     |    2.5                |    2.5