把客户按城市排序，城市缺失的客户放在最后。
- 先按
city升序（按字符串的字节序比较，数据里的城市名都是首字母大写的英文）； city为 null 的客户排在最后；- 城市相同（包括都为 null）时按
customer_id升序。
输入
customers(customer_id, name, email, city, signup_date, tier)
输出
列为 customer_id, name, city，行顺序必须与上面的排序规则一致。
null 排最后
输入表 （case base，共 2 个 case：base、scrambled）
customers shop/customers
| # | customer_idint64 | namestring | emailstring | citystring | signup_datedate | tierstring |
|---|---|---|---|---|---|---|
| 1 | 1 | Fang Wang | fang.wang@shop.io | Beijing | 2025-03-13 | silver |
| 2 | 2 | Dana Xu | dana.xu@mail.cn | null | 2025-02-17 | silver |
| 3 | 3 | Li Zhou | li.zhou@example.com | Guangzhou | 2025-10-07 | bronze |
| 4 | 4 | Ping Wang | ping.wang@example.com | null | 2025-05-23 | gold |
| 5 | 5 | Tom Zhang | tom.zhang@example.com | Shenzhen | 2025-06-26 | gold |
| 6 | 6 | 王芳 | user06@shop.io | Hangzhou | 2025-02-10 | gold |
| 7 | 7 | Victor Xu | victor.xu@example.com | Shanghai | 2025-12-05 | bronze |
| 8 | 8 | Dana Chen | dana.chen@example.com | Hangzhou | 2025-11-22 | bronze |
| 9 | 9 | Uma Chen | uma.chen@shop.io | Guangzhou | 2025-11-28 | null |
| 10 | 10 | Ivy Zhou | ivy.zhou@shop.io | Hangzhou | 2025-07-14 | gold |
| 11 | 11 | Mia Smith | mia.smith@mail.cn | Shanghai | 2025-04-28 | gold |
| 12 | 12 | Xin Yang | xin.yang@example.com | Chengdu | 2026-01-03 | silver |
| 13 | 13 | Xin Smith | xin.smith@mail.cn | Beijing | 2025-05-07 | silver |
| 14 | 14 | Zoe Xu | zoe.xu@mail.cn | Beijing | 2025-09-18 | silver |
| 15 | 15 | Fang Liu | fang.liu@shop.io | Guangzhou | 2025-08-05 | bronze |
| 16 | 16 | 杨磊 | user16@mail.cn | Shanghai | 2025-12-15 | silver |
| 17 | 17 | Ping Smith | ping.smith@mail.cn | null | 2025-08-11 | bronze |
| 18 | 18 | Oscar Zhou | oscar.zhou@example.com | Shanghai | 2025-11-17 | null |
| 19 | 19 | Kevin Liu | kevin.liu@mail.cn | Chengdu | 2026-02-03 | gold |
| 20 | 20 | Sara Wu | sara.wu@example.com | null | 2025-07-05 | gold |
显示前 20 行，共 50 行
期望输出 （case base，行顺序要一致）
| # | customer_idInt64 | nameString | cityString |
|---|---|---|---|
| 1 | 1 | Fang Wang | Beijing |
| 2 | 13 | Xin Smith | Beijing |
| 3 | 14 | Zoe Xu | Beijing |
| 4 | 43 | Rui Smith | Beijing |
| 5 | 50 | Hao Chen | Beijing |
| 6 | 12 | Xin Yang | Chengdu |
| 7 | 19 | Kevin Liu | Chengdu |
| 8 | 21 | Rui Chen | Chengdu |
| 9 | 22 | 刘洋 | Chengdu |
| 10 | 23 | 李娜 | Chengdu |
| 11 | 31 | Nina Zhang | Chengdu |
| 12 | 34 | Qing Zhao | Chengdu |
| 13 | 35 | Qing Chen | Chengdu |
| 14 | 36 | 陈静 | Chengdu |
| 15 | 37 | Chen Smith | Chengdu |
| 16 | 38 | Dana Zhao | Chengdu |
| 17 | 40 | Chen Wang | Chengdu |
| 18 | 42 | Ivy Wu | Chengdu |
| 19 | 47 | Fang Zhang | Chengdu |
| 20 | 3 | Li Zhou | Guangzhou |
| 21 | 9 | Uma Chen | Guangzhou |
| 22 | 15 | Fang Liu | Guangzhou |
| 23 | 24 | Kevin Lee | Guangzhou |
| 24 | 39 | Sara Chen | Guangzhou |
| 25 | 6 | 王芳 | Hangzhou |
| 26 | 8 | Dana Chen | Hangzhou |
| 27 | 10 | Ivy Zhou | Hangzhou |
| 28 | 32 | Wei Zhang | Hangzhou |
| 29 | 46 | Grace Smith | Hangzhou |
| 30 | 7 | Victor Xu | Shanghai |
| 31 | 11 | Mia Smith | Shanghai |
| 32 | 16 | 杨磊 | Shanghai |
| 33 | 18 | Oscar Zhou | Shanghai |
| 34 | 25 | 张伟 | Shanghai |
| 35 | 28 | Nina Wu | Shanghai |
| 36 | 29 | Bob Smith | Shanghai |
| 37 | 5 | Tom Zhang | Shenzhen |
| 38 | 27 | Amy Huang | Shenzhen |
| 39 | 41 | Lin Zhou | Shenzhen |
| 40 | 44 | Eric Lee | Shenzhen |
| 41 | 45 | Oscar Wang | Shenzhen |
| 42 | 49 | Lin Smith | Shenzhen |
| 43 | 2 | Dana Xu | null |
| 44 | 4 | Ping Wang | null |
| 45 | 17 | Ping Smith | null |
| 46 | 20 | Sara Wu | null |
| 47 | 26 | Mia Xu | null |
| 48 | 30 | Eric Chen | null |
| 49 | 33 | Bob Liu | null |
| 50 | 48 | Hao Zhao | null |
共 50 行