orders 表的 channel 列有缺失。把 channel 为 null 的值填成字符串 unknown，其余列保持不变。
channel：其他列（例如 customer_id、status、order_ts）里的 null 要原样保留。"" 不是 null，保持为空字符串。输入
orders(order_id, customer_id, order_ts, status, channel)输出
列为 order_id, customer_id, order_ts, status, channel，行数与输入相同，行顺序不限。
orders shop/orders
| # | order_idint64 | customer_idint64 | order_tsdatetime | statusstring | channelstring |
|---|---|---|---|---|---|
| 1 | 1001 | 39 | 2026-01-01 19:38:00 | paid | app |
| 2 | 1002 | 16 | 2026-01-17 14:07:00 | paid | app |
| 3 | 1003 | 4 | 2026-01-08 15:40:20 | cancelled | web |
| 4 | 1004 | 2 | 2026-05-23 10:48:58 | paid | null |
| 5 | 1005 | 12 | 2026-06-22 11:07:22 | paid | store |
| 6 | 1006 | 17 | 2026-08-15 05:15:25 | paid | web |
| 7 | 1007 | 9 | 2026-06-11 01:00:32 | refunded | store |
| 8 | 1008 | 45 | 2026-09-19 20:47:10 | paid | web |
| 9 | 1009 | 2 | 2025-10-05 04:53:38 | paid | app |
| 10 | 1010 | 4 | 2026-02-19 01:39:54 | paid | app |
| 11 | 1011 | 28 | 2026-03-05 03:04:45 | refunded | store |
| 12 | 1012 | 2 | 2026-08-01 07:09:17 | paid | web |
| 13 | 1013 | 26 | 2026-01-22 03:48:14 | refunded | store |
| 14 | 1014 | 2 | 2026-02-09 01:41:41 | paid | app |
| 15 | 1015 | 5 | 2026-08-03 19:49:04 | refunded | web |
| 16 | 1016 | 26 | 2026-02-16 00:43:43 | refunded | app |
| 17 | 1017 | 9 | 2025-12-06 04:48:57 | pending | app |
| 18 | 1018 | 999 | 2026-05-19 12:13:43 | paid | store |
| 19 | 1019 | 26 | 2026-02-05 15:02:26 | paid | store |
| 20 | 1020 | 44 | 2025-11-24 11:19:00 | cancelled | web |
| # | order_idInt64 | customer_idInt64 | order_tsDatetime(time_unit='us', time_zone=None) | statusString | channelString |
|---|---|---|---|---|---|
| 1 | 1001 | 39 | 2026-01-01 19:38:00 | paid | app |
| 2 | 1002 | 16 | 2026-01-17 14:07:00 | paid | app |
| 3 | 1003 | 4 | 2026-01-08 15:40:20 | cancelled | web |
| 4 | 1004 | 2 | 2026-05-23 10:48:58 | paid | unknown |
| 5 | 1005 | 12 | 2026-06-22 11:07:22 | paid | store |
| 6 | 1006 | 17 | 2026-08-15 05:15:25 | paid | web |
| 7 | 1007 | 9 | 2026-06-11 01:00:32 | refunded | store |
| 8 | 1008 | 45 | 2026-09-19 20:47:10 | paid | web |
| 9 | 1009 | 2 | 2025-10-05 04:53:38 | paid | app |
| 10 | 1010 | 4 | 2026-02-19 01:39:54 | paid | app |
| 11 | 1011 | 28 | 2026-03-05 03:04:45 | refunded | store |
| 12 | 1012 | 2 | 2026-08-01 07:09:17 | paid | web |
| 13 | 1013 | 26 | 2026-01-22 03:48:14 | refunded | store |
| 14 | 1014 | 2 | 2026-02-09 01:41:41 | paid | app |
| 15 | 1015 | 5 | 2026-08-03 19:49:04 | refunded | web |
| 16 | 1016 | 26 | 2026-02-16 00:43:43 | refunded | app |
| 17 | 1017 | 9 | 2025-12-06 04:48:57 | pending | app |
| 18 | 1018 | 999 | 2026-05-19 12:13:43 | paid | store |
| 19 | 1019 | 26 | 2026-02-05 15:02:26 | paid | store |
| 20 | 1020 | 44 | 2025-11-24 11:19:00 | cancelled | web |
| 21 | 1021 | 18 | 2026-06-29 17:32:41 | refunded | app |
| 22 | 1022 | 1 | 2026-06-23 06:27:44 | cancelled | app |
| 23 | 1023 | 46 | 2026-07-24 02:09:45 | refunded | web |
| 24 | 1024 | 47 | 2026-02-26 18:42:02 | paid | unknown |
| 25 | 1025 | 34 | 2026-07-05 07:41:49 | cancelled | web |
| 26 | 1026 | 18 | 2025-11-24 08:15:00 | paid | web |
| 27 | 1027 | 42 | 2026-05-22 08:52:21 | paid | web |
| 28 | 1028 | 36 | 2026-01-12 18:12:02 | paid | app |
| 29 | 1029 | 18 | 2026-03-03 14:01:10 | paid | web |
| 30 | 1030 | 5 | 2026-06-12 16:22:09 | paid | store |
| 31 | 1031 | 5 | 2026-02-14 10:30:00 | paid | app |
| 32 | 1032 | 5 | 2026-02-14 13:30:00 | paid | web |
| 33 | 1033 | 5 | 2026-02-14 16:30:00 | paid | store |
| 34 | 1034 | 5 | 2026-02-14 10:30:00 | paid | app |
| 35 | 1035 | 24 | 2025-12-25 18:50:00 | refunded | unknown |
| 36 | 1036 | 14 | 2026-01-16 01:42:07 | refunded | app |
| 37 | 1037 | 38 | 2026-03-08 19:28:41 | pending | store |
| 38 | 1038 | 9 | 2025-12-18 09:01:58 | paid | store |
| 39 | 1039 | 2 | 2025-09-12 08:26:19 | paid | web |
| 40 | 1040 | 12 | 2026-02-11 15:04:00 | cancelled | web |
| 41 | 1041 | 32 | 2026-04-22 15:13:08 | paid | app |
| 42 | 1042 | 35 | 2025-10-28 14:44:18 | cancelled | web |
| 43 | 1043 | 26 | 2026-01-05 21:57:00 | paid | store |
| 44 | 1044 | 6 | 2026-02-09 18:36:53 | paid | store |
| 45 | 1045 | 45 | 2026-01-23 07:06:47 | cancelled | web |
| 46 | 1046 | 22 | 2026-06-30 01:58:03 | paid | web |
| 47 | 1047 | 8 | 2026-01-09 09:26:50 | paid | app |
| 48 | 1048 | 5 | 2025-12-14 00:07:09 | paid | app |
| 49 | 1049 | 44 | 2026-07-31 23:48:12 | paid | app |
| 50 | 1050 | 34 | 2026-01-05 17:34:00 | refunded | unknown |