SELECT cust_id,cust_name, upper(concat(substring(cust_name,1,2),substring(cust_city,1,3))) AS user_login FROM Customers /*substring(截取的字符串,起始位置,终止位置) 和substringindex(截取的字符串,以什么来截取,截取到哪个位置) concat(字符串1,2)*/