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选出指定列

简单 01-select 选择与投影 selectprojection

从客户表里只取出客户编号、姓名和城市三列。

  • 按列名取列，不要依赖列在表里的位置：第二个 case 里的表列顺序与第一个不同。
  • 所有行都保留，city 为 null 的行也保留。

输入

  • customers(customer_id, name, email, city, signup_date, tier)（列的先后顺序因 case 而异）

输出

列为 customer_id, name, city，行顺序不限。

输入表 （case base，共 2 个 case：base、reordered）

customers shop/customers
#customer_idint64namestringemailstringcitystringsignup_datedatetierstring
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，行顺序不限）

#customer_idInt64nameStringcityString
1 1 Fang Wang Beijing
2 2 Dana Xu null
3 3 Li Zhou Guangzhou
4 4 Ping Wang null
5 5 Tom Zhang Shenzhen
6 6 王芳 Hangzhou
7 7 Victor Xu Shanghai
8 8 Dana Chen Hangzhou
9 9 Uma Chen Guangzhou
10 10 Ivy Zhou Hangzhou
11 11 Mia Smith Shanghai
12 12 Xin Yang Chengdu
13 13 Xin Smith Beijing
14 14 Zoe Xu Beijing
15 15 Fang Liu Guangzhou
16 16 杨磊 Shanghai
17 17 Ping Smith null
18 18 Oscar Zhou Shanghai
19 19 Kevin Liu Chengdu
20 20 Sara Wu null
21 21 Rui Chen Chengdu
22 22 刘洋 Chengdu
23 23 李娜 Chengdu
24 24 Kevin Lee Guangzhou
25 25 张伟 Shanghai
26 26 Mia Xu null
27 27 Amy Huang Shenzhen
28 28 Nina Wu Shanghai
29 29 Bob Smith Shanghai
30 30 Eric Chen null
31 31 Nina Zhang Chengdu
32 32 Wei Zhang Hangzhou
33 33 Bob Liu null
34 34 Qing Zhao Chengdu
35 35 Qing Chen Chengdu
36 36 陈静 Chengdu
37 37 Chen Smith Chengdu
38 38 Dana Zhao Chengdu
39 39 Sara Chen Guangzhou
40 40 Chen Wang Chengdu
41 41 Lin Zhou Shenzhen
42 42 Ivy Wu Chengdu
43 43 Rui Smith Beijing
44 44 Eric Lee Shenzhen
45 45 Oscar Wang Shenzhen
46 46 Grace Smith Hangzhou
47 47 Fang Zhang Chengdu
48 48 Hao Zhao null
49 49 Lin Smith Shenzhen
50 50 Hao Chen Beijing
共 50 行