题解 | #顾客登录名#

select 
cust_id,
cust_name,
upper(concat(substring(cust_contact,1,2),substring(cust_city,1,3))) as user_login
from Customers;
-- substring 从开始项截取所需字符串个数
-- 如：select  substring('hello mysql ',2,5)；#返回ello
/*方法二*/
select cust_id,cust_name,
upper(concat(left(cust_contact,2),left(cust_city,3))) 
as user_login
from Customers;
/*
upper():小写转大写
concat(s1,s2):连接两个字符串
left(column_name,int size):取字符串左边 size个字符
*/