题解 | 顾客登录名

WITH joint AS (
    -- 子查询部分，将所需要的信息截取出来
    SELECT
        cust_id,
        cust_name,
        SUBSTRING(cust_name, 1, 2) AS first_two_chars_of_name, -- 联系人取前两个字符
        SUBSTRING(cust_city, 1, 3) AS first_three_chars_of_city -- 所在城市取前三个字符
    FROM
        Customers
    )

-- 主查询部分，输出顾客id，顾客名称和顾客登录名
SELECT
    cust_id,
    cust_name,
    UPPER(CONCAT(first_two_chars_of_name, first_three_chars_of_city)) AS user_login -- 合并且转大写
FROM
    joint
;