select cust_id,
cust_name,
#upper(concat(left(cust_name,2),left(cust_city,3))) as user_login
upper(concat(substring(cust_name,1,2),substring(cust_city,1,3))) as user_login
from Customers
 拼接concat
字符串相关函数 upper转大写，lower小写
substring 子字符串
left/right返回从左、右开始对应个数字符串