客户导出表里用了几种“哨兵值”表示缺失。清洗 email 和 phone 两列：
N/A、空字符串 "" 或 -，就变成 null。比较区分大小写，必须完全相等（n/a、--、N / A 都不算哨兵值）。id 原样输出（id 可能重复，重复的行照常输出）。
输入
raw_customers(id, full_name, email, phone, birthday, signup, vip, spend)，所有列都是字符串。输出
列为 id, email, phone，行数与输入相同，行顺序不限。
raw_customers messy/raw_customers
| # | idstring | full_namestring | emailstring | phonestring | birthdaystring | signupstring | vipstring | spendstring |
|---|---|---|---|---|---|---|---|---|
| 1 | 1 | xu ming | xu.ming60@mail.cn | +86 189 3287 9217 | - | 2025-02-12 | YES | 3428 |
| 2 | 2 | yang guo | yang.guo68@example.com | 10033907579 | 2003-04-21 | 05/01/2025 | n | 2,132.69 |
| 3 | 3 | guo jing | guo.jing91@mail.cn | 15384019161 | 01/02/1994 | 2025-01-01 | Y | 3716.67 |
| 4 | 4 | zhou jie | zhou.jie26@qq.com | 14514506123 | 29/02/2000 | 01/07/2025 | no | 999.73 |
| 5 | 5 | liu yang | liu.yang51@mail.cn | 13049403 | 31/04/1999 | 2025-09-22 | 0 | 2024 |
| 6 | 6 | zhang san | ZHANG.SAN@Example.COM | 13095597297 | 06/07/1978 | 15/11/2025 | no | $1,200.50 |
| 7 | 7 | null | zhou.jie54@example.com | (111) 08436469 | 2003.3.24 | 2025-08-22 | N | $4,809.60 |
| 8 | 8 | BOB smith | N/A | 173-0024-5892 | 11/08/1978 | 2026-06-19 | yes | 4842.25 |
| 9 | 9 | LI WEI | li.wei40@example.com | (109) 17145211 | - | 13/05/2025 | 0 | 3592.13 |
| 10 | 10 | he ping | he.ping54@example.com | 179-0966-9091 | 14/05/1977 | 02/02/2026 | n | 4395.47 |
| 11 | 11 | guo jing | guo.jing4@mail.cn | 19170317974 | 05/05/1993 | 2025-07-27 | 0 | 2,316.99 |
| 12 | 12 | he ping | he.ping86@mail.cn | 136-3363-9532 | 1992-01-23 | 11/10/2025 | N | 1442.64 |
| 13 | 13 | BOB smith | bob.smith67@mail.cn | 1971-11-05 | 2025-07-14 | 1 | $738.58 | |
| 14 | 14 | WANG FANG | wang.fang@@mail.com | N/A | 09/04/1981 | 07/07/2026 | yes | 4152.00 |
| 15 | 15 | grace HOPPER | grace.hopper93@mail.cn | (127) 73068985 | - | 2025-05-07 | YES | 1624 |
| 16 | 16 | guo jing | guo.jing34@qq.com | (105) 81075864 | 2025-02-05 | 0 | 4,802.51 | |
| 17 | 17 | LIU YANG | liu.yang93@qq.com | 17791378 | 16/11/2025 | no | 740.03 | |
| 18 | 18 | GUO JING | guo.jing26@mail.cn | 18180960808 | 04/10/2004 | 2025-06-20 | n | 4196.37 |
| 19 | 19 | zhou jie | zhou.jie17@mail.cn | 167-8513-6904 | 1971-01-07 | 13/01/2025 | 0 | free |
| 20 | 20 | CHEN JING | chen.jing66@qq.com | - | 28/04/2003 | 2025-05-20 | 0 | 1656 |
| # | idString | emailString | phoneString |
|---|---|---|---|
| 1 | 1 | xu.ming60@mail.cn | +86 189 3287 9217 |
| 2 | 2 | yang.guo68@example.com | 10033907579 |
| 3 | 3 | guo.jing91@mail.cn | 15384019161 |
| 4 | 4 | zhou.jie26@qq.com | 14514506123 |
| 5 | 5 | liu.yang51@mail.cn | 13049403 |
| 6 | 6 | ZHANG.SAN@Example.COM | 13095597297 |
| 7 | 7 | zhou.jie54@example.com | (111) 08436469 |
| 8 | 8 | null | 173-0024-5892 |
| 9 | 9 | li.wei40@example.com | (109) 17145211 |
| 10 | 10 | he.ping54@example.com | 179-0966-9091 |
| 11 | 11 | guo.jing4@mail.cn | 19170317974 |
| 12 | 12 | he.ping86@mail.cn | 136-3363-9532 |
| 13 | 13 | bob.smith67@mail.cn | null |
| 14 | 14 | wang.fang@@mail.com | null |
| 15 | 15 | grace.hopper93@mail.cn | (127) 73068985 |
| 16 | 16 | guo.jing34@qq.com | (105) 81075864 |
| 17 | 17 | liu.yang93@qq.com | 17791378 |
| 18 | 18 | guo.jing26@mail.cn | 18180960808 |
| 19 | 19 | zhou.jie17@mail.cn | 167-8513-6904 |
| 20 | 20 | chen.jing66@qq.com | null |
| 21 | 21 | yang.guo28@example.com | null |
| 22 | 22 | chen.jing44@qq.com | (131) 71008989 |
| 23 | 23 | xu.ming@@mail.com | 168-5639-5003 |
| 24 | 24 | zhao.lei91@qq.com | 16993895441 |
| 25 | 25 | amy.chen61@example.com | null |
| 26 | 26 | grace.hopper7@example.com | (160) 14445888 |
| 27 | 27 | wang.fang50@mail.cn | null |
| 28 | 28 | ada.lovelace75@example.com | 12660560951 |
| 29 | 29 | xu.ming32@qq.com | 110-9671-3058 |
| 30 | 30 | ma.yun@@mail.com | +86 123 7184 8954 |
| 31 | 31 | wang.fang4@qq.com | 10138411 |
| 32 | 32 | chen.jing28@mail.cn | 16462529548 |
| 33 | 33 | wu.han88@mail.cn | +86 140 1439 1475 |
| 34 | 34 | huang.rong88@mail.cn | (178) 47536831 |
| 35 | 35 | guo.jing23@example.com | +86 117 4038 0829 |
| 36 | 36 | zhang.san@@mail.com | (102) 16337857 |
| 37 | 37 | wu.han45@example.com | 16178085016 |
| 38 | 38 | ma.yun8@mail.cn | 14142207097 |
| 39 | 39 | yang.guo36@mail.cn | 12488747658 |
| 40 | 40 | ma.yun8@qq.com | 130-7573-6926 |
| 41 | 41 | LIU.YANG@Example.COM | 13221549817 |
| 42 | 42 | zhang.san5@qq.com | +86 168 7245 4618 |
| 43 | 43 | xu.ming16@qq.com | 17067349170 |
| 44 | 44 | zhou.jie@@mail.com | 161-5449-7576 |
| 45 | 45 | huang.rong@@mail.com | 11661568232 |
| 46 | 46 | grace.hopper3@mail.cn | +86 153 5471 8638 |
| 47 | 47 | yang.guo.mail.com | (183) 90312379 |
| 48 | 48 | liu.yang70@qq.com | 11842592104 |
| 49 | 49 | amy.chen85@example.com | 146-9902-3670 |
| 50 | 50 | zhao.lei93@qq.com | 12679175699 |