select cust_id, cust_name, upper(concat(substring(cust_contact, 1, 2), substring(cust_city, 1, 3))) user_login from Customers # 大写字母转换函数upper # 拼接函数concat # 获取每列前几个字符substring(columnname, 第几个字符开始, 获取前几个字符)