我有一个创建瀑布的查询：
SELECT CONCAT(SUBSTR(snapshot_date, -4, 4),'-',SUBSTR(snapshot_date, -10, 2),'-', SUBSTR(snapshot_date, -7, 2)) snapshot,
item_name,
type,
translated_order_type,
item_description,
source_plan,
week_start_date,
qty
FROM A
WHERE
concat(SUBSTR(snapshot_date, -4, 4),'-',SUBSTR(snapshot_date, -10, 2),'-', SUBSTR(snapshot_date, -7, 2)) >=
strftime_usec(date_add(TIME_USEC_TO_WEEK(date_add(now(),-84,'DAY'),1),-1,'DAY'),'%Y-%m-%d')
结果如下所示:(在excel中创建数据透视表后，并不是完整图片）
week_start_date
+------------+--------+--------+---------+---------+---------+---------+----------+
| snapshot | 9/1/14 | 9/8/14 | 9/15/14 | 9/22/14 | 9/29/14 | 10/6/14 | 10/13/14 |
+------------+--------+--------+---------+---------+---------+---------+----------+
| 8/31/14 | 380 | 97 | 104 | 84 | 84 | 76 | 81 |
| 9/7/14 | | 378 | 91 | 89 | 96 | 90 | 108 |
| 9/14/14 | | | 203 | 31 | 27 | 30 | 41 |
| 9/21/14 | | | | 405 | 111 | 75 | 77 |
| 9/28/14 | | | | | 436 | 73 | 93 |
| 10/5/14 | | | | | | 433 | 93 |
| 10/14/14 | | | | | | | 439 |
+------------+--------+--------+---------+---------+---------+---------+----------+
行标签（8/31 / 14,19 / 7/14等）是快照日期，列标签是week_start_date。结果看起来是因为每个快照日期在此日期都有关于项目的数量和其他信息，并且每个快照日期将在不同周内具有数量，即week_start_date。
这里的空白是因为每个快照日期只有快照日期或超出快照日期的数量。
e.g. snapshot 8/31/14 will have week_start_date from 9/1/14 to 10/31/14,
snapshot 9/7/14 will have week_start_date from 9/8/14 to 10/20/14,
snapshot 9/14/13 will have week_start_date from 9/15/14 to 10/27/14
我需要在bigquery sql中执行此操作，以填充那些没有上一个week_start_date的快照的week_start_date。意味着所有快照日期都具有相同的week_start_date集。（min将是最早的快照，max将是最新的快照。）我不知道该怎么做。
谢谢！
数据样本：
+----------+-----------+---------------------+------+
| snapshot | item_name | sdm_week_start_date | qty |
+----------+-----------+---------------------+------+
| 11/9/14 | 86001741 | 11/10/14 | 512 |
| 11/9/14 | 86001741 | 11/10/14 | 1492 |
| 11/9/14 | 86001741 | 11/10/14 | 53 |
| 11/16/14 | 86001741 | 11/17/14 | 704 |
| 11/16/14 | 86001741 | 11/17/14 | 49 |
| 11/16/14 | 86001741 | 11/17/14 | 1665 |
| 11/16/14 | 86001741 | 11/17/14 | 384 |
| 11/16/14 | 86001741 | 11/17/14 | 32 |
| 11/9/14 | 86001741 | 11/17/14 | 156 |
| 11/9/14 | 86001741 | 11/17/14 | 1 |
| 11/9/14 | 86001741 | 11/24/14 | 152 |
| 11/16/14 | 86001741 | 11/24/14 | 192 |
| 11/23/14 | 86001741 | 11/24/14 | 1683 |
| 11/16/14 | 86001741 | 11/24/14 | 24 |
| 11/23/14 | 86001741 | 11/24/14 | 49 |
| 11/16/14 | 86001741 | 11/24/14 | 152 |
| 11/23/14 | 86001741 | 11/24/14 | 1280 |
| 11/23/14 | 86001741 | 11/24/14 | 96 |
| 11/23/14 | 86001741 | 12/1/14 | 156 |
| 11/9/14 | 86001741 | 12/1/14 | 156 |
| 11/16/14 | 86001741 | 12/1/14 | 156 |
| 11/23/14 | 86001741 | 12/8/14 | 220 |
| 11/9/14 | 86001741 | 12/8/14 | 178 |
| 11/16/14 | 86001741 | 12/8/14 | 220 |
| 11/9/14 | 86001741 | 12/15/14 | 178 |
| 11/23/14 | 86001741 | 12/15/14 | 220 |
| 11/16/14 | 86001741 | 12/15/14 | 220 |
| 11/23/14 | 86001741 | 12/22/14 | 221 |
| 11/9/14 | 86001741 | 12/22/14 | 179 |
| 11/23/14 | 86001741 | 12/22/14 | 64 |
| 11/9/14 | 86001741 | 12/22/14 | 504 |
| 11/23/14 | 86001741 | 12/22/14 | 552 |
| 11/9/14 | 86001741 | 12/22/14 | 768 |
| 11/16/14 | 86001741 | 12/22/14 | 221 |
| 11/16/14 | 86001741 | 12/22/14 | 1024 |
| 11/16/14 | 86001741 | 12/22/14 | 552 |
| 11/9/14 | 86001741 | 12/22/14 | 64 |
| 11/16/14 | 86001741 | 12/22/14 | 64 |
| 11/23/14 | 86001741 | 12/22/14 | 1024 |
| 11/23/14 | 86001741 | 12/29/14 | 220 |
| 11/16/14 | 86001741 | 12/29/14 | 220 |
| 11/9/14 | 86001741 | 12/29/14 | 178 |
| 11/16/14 | 86001741 | 1/5/15 | 221 |
| 11/23/14 | 86001741 | 1/5/15 | 221 |
| 11/9/14 | 86001741 | 1/5/15 | 221 |
| 11/23/14 | 86001741 | 1/12/15 | 216 |
| 11/16/14 | 86001741 | 1/12/15 | 216 |
| 11/9/14 | 86001741 | 1/12/15 | 216 |
| 11/16/14 | 86001741 | 1/19/15 | 218 |
| 11/16/14 | 86001741 | 1/19/15 | 5 |
| 11/23/14 | 86001741 | 1/19/15 | 32 |
| 11/9/14 | 86001741 | 1/19/15 | 1280 |
| 11/23/14 | 86001741 | 1/19/15 | 408 |
| 11/9/14 | 86001741 | 1/19/15 | 480 |
| 11/9/14 | 86001741 | 1/19/15 | 5 |
| 11/9/14 | 86001741 | 1/19/15 | 218 |
| 11/16/14 | 86001741 | 1/19/15 | 32 |
| 11/23/14 | 86001741 | 1/19/15 | 1152 |
| 11/23/14 | 86001741 | 1/19/15 | 10 |
| 11/9/14 | 86001741 | 1/19/15 | 64 |
| 11/16/14 | 86001741 | 1/19/15 | 408 |
| 11/23/14 | 86001741 | 1/19/15 | 218 |
| 11/16/14 | 86001741 | 1/19/15 | 1152 |
| 11/9/14 | 86001741 | 1/26/15 | 216 |
| 11/23/14 | 86001741 | 1/26/15 | 216 |
| 11/16/14 | 86001741 | 1/26/15 | 216 |
| 11/9/14 | 86001741 | 2/2/15 | 112 |
| 11/16/14 | 86001741 | 2/2/15 | 112 |
| 11/23/14 | 86001741 | 2/2/15 | 143 |
| 11/23/14 | 86001741 | 2/9/15 | 156 |
| 11/16/14 | 86001741 | 2/9/15 | 124 |
| 11/9/14 | 86001741 | 2/9/15 | 124 |
| 11/9/14 | 86001741 | 2/16/15 | 256 |
| 11/23/14 | 86001741 | 2/16/15 | 896 |
| 11/9/14 | 86001741 | 2/16/15 | 120 |
| 11/16/14 | 86001741 | 2/16/15 | 127 |
| 11/23/14 | 86001741 | 2/16/15 | 158 |
| 11/16/14 | 86001741 | 2/16/15 | 12 |
| 11/23/14 | 86001741 | 2/16/15 | 216 |
| 11/9/14 | 86001741 | 2/16/15 | 127 |
| 11/23/14 | 86001741 | 2/16/15 | 12 |
| 11/16/14 | 86001741 | 2/16/15 | 216 |
| 11/16/14 | 86001741 | 2/16/15 | 896 |
| 11/9/14 | 86001741 | 2/16/15 | 12 |
| 11/9/14 | 86001741 | 2/23/15 | 124 |
| 11/16/14 | 86001741 | 2/23/15 | 124 |
| 11/23/14 | 86001741 | 2/23/15 | 156 |
| 11/16/14 | 86001741 | 3/2/15 | 252 |
| 11/23/14 | 86001741 | 3/2/15 | 242 |
| 11/9/14 | 86001741 | 3/2/15 | 252 |
| 11/9/14 | 86001741 | 3/9/15 | 250 |
| 11/16/14 | 86001741 | 3/9/15 | 250 |
| 11/23/14 | 86001741 | 3/9/15 | 240 |
| 11/9/14 | 86001741 | 3/16/15 | 12 |
| 11/16/14 | 86001741 | 3/16/15 | 257 |
| 11/23/14 | 86001741 | 3/16/15 | 12 |
| 11/9/14 | 86001741 | 3/16/15 | 257 |
| 11/23/14 | 86001741 | 3/16/15 | 247 |
| 11/16/14 | 86001741 | 3/16/15 | 12 |
| 11/16/14 | 86001741 | 3/23/15 | 32 |
| 11/23/14 | 86001741 | 3/23/15 | 32 |
| 11/9/14 | 86001741 | 3/23/15 | 255 |
| 11/16/14 | 86001741 | 3/23/15 | 216 |
| 11/16/14 | 86001741 | 3/23/15 | 768 |
| 11/16/14 | 86001741 | 3/23/15 | 255 |
| 11/23/14 | 86001741 | 3/23/15 | 245 |
| 11/23/14 | 86001741 | 3/23/15 | 768 |
| 11/9/14 | 86001741 | 3/23/15 | 32 |
| 11/23/14 | 86001741 | 3/23/15 | 216 |
| 11/9/14 | 86001741 | 3/23/15 | 168 |
| 11/9/14 | 86001741 | 3/23/15 | 384 |
| 11/9/14 | 86001741 | 3/30/15 | 257 |
| 11/23/14 | 86001741 | 3/30/15 | 247 |
| 11/16/14 | 86001741 | 3/30/15 | 257 |
| 11/9/14 | 86001741 | 4/6/15 | 314 |
| 11/23/14 | 86001741 | 4/6/15 | 302 |
| 11/16/14 | 86001741 | 4/6/15 | 314 |
| 11/16/14 | 86001741 | 4/13/15 | 5 |
| 11/16/14 | 86001741 | 4/13/15 | 304 |
| 11/23/14 | 86001741 | 4/13/15 | 5 |
| 11/23/14 | 86001741 | 4/13/15 | 291 |
| 11/9/14 | 86001741 | 4/13/15 | 5 |
| 11/9/14 | 86001741 | 4/13/15 | 304 |
| 11/9/14 | 86001741 | 4/20/15 | 144 |
| 11/23/14 | 86001741 | 4/20/15 | 192 |
| 11/23/14 | 86001741 | 4/20/15 | 32 |
| 11/16/14 | 86001741 | 4/20/15 | 192 |
| 11/23/14 | 86001741 | 4/20/15 | 448 |
| 11/16/14 | 86001741 | 4/20/15 | 32 |
| 11/16/14 | 86001741 | 4/20/15 | 302 |
| 11/9/14 | 86001741 | 4/20/15 | 32 |
| 11/9/14 | 86001741 | 4/20/15 | 302 |
| 11/23/14 | 86001741 | 4/20/15 | 290 |
| 11/9/14 | 86001741 | 4/20/15 | 320 |
| 11/16/14 | 86001741 | 4/20/15 | 448 |
| 11/16/14 | 86001741 | 4/27/15 | 304 |
| 11/9/14 | 86001741 | 4/27/15 | 304 |
| 11/23/14 | 86001741 | 4/27/15 | 291 |
| 11/16/14 | 86001741 | 5/4/15 | 156 |
| 11/9/14 | 86001741 | 5/4/15 | 156 |
| 11/23/14 | 86001741 | 5/4/15 | 150 |
| 11/23/14 | 86001741 | 5/11/15 | 142 |
| 11/9/14 | 86001741 | 5/11/15 | 149 |
| 11/16/14 | 86001741 | 5/11/15 | 149 |
| 11/16/14 | 86001741 | 5/18/15 | 5 |
| 11/23/14 | 86001741 | 5/18/15 | 140 |
| 11/23/14 | 86001741 | 5/18/15 | 5 |
| 11/9/14 | 86001741 | 5/18/15 | 5 |
| 11/9/14 | 86001741 | 5/18/15 | 146 |
| 11/16/14 | 86001741 | 5/18/15 | 146 |
| 11/16/14 | 86001741 | 5/25/15 | 48 |
| 11/9/14 | 86001741 | 5/25/15 | 149 |
| 11/23/14 | 86001741 | 5/25/15 | 142 |
| 11/16/14 | 86001741 | 5/25/15 | 128 |
| 11/23/14 | 86001741 | 5/25/15 | 48 |
| 11/16/14 | 86001741 | 5/25/15 | 149 |
| 11/9/14 | 86001741 | 5/25/15 | 48 |
| 11/9/14 | 86001741 | 5/25/15 | 128 |
| 11/23/14 | 86001741 | 5/25/15 | 128 |
| 11/9/14 | 86001741 | 6/1/15 | 197 |
| 11/23/14 | 86001741 | 6/1/15 | 197 |
| 11/16/14 | 86001741 | 6/1/15 | 197 |
| 11/9/14 | 86001741 | 6/8/15 | 198 |
| 11/23/14 | 86001741 | 6/8/15 | 198 |
| 11/16/14 | 86001741 | 6/8/15 | 198 |
| 11/16/14 | 86001741 | 6/15/15 | 198 |
| 11/16/14 | 86001741 | 6/15/15 | 5 |
| 11/23/14 | 86001741 | 6/15/15 | 198 |
| 11/9/14 | 86001741 | 6/15/15 | 198 |
| 11/9/14 | 86001741 | 6/15/15 | 5 |
| 11/23/14 | 86001741 | 6/15/15 | 5 |
| 11/23/14 | 86001741 | 6/22/15 | 198 |
| 11/9/14 | 86001741 | 6/22/15 | 198 |
| 11/16/14 | 86001741 | 6/22/15 | 198 |
| 11/23/14 | 86001741 | 6/29/15 | 198 |
| 11/9/14 | 86001741 | 6/29/15 | 198 |
| 11/16/14 | 86001741 | 6/29/15 | 198 |
| 11/23/14 | 86001741 | 7/6/15 | 247 |
| 11/16/14 | 86001741 | 7/6/15 | 247 |
| 11/9/14 | 86001741 | 7/6/15 | 247 |
| 11/16/14 | 86001741 | 7/13/15 | 245 |
| 11/23/14 | 86001741 | 7/13/15 | 245 |
| 11/9/14 | 86001741 | 7/13/15 | 245 |
| 11/16/14 | 86001741 | 7/20/15 | 246 |
| 11/9/14 | 86001741 | 7/20/15 | 246 |
| 11/23/14 | 86001741 | 7/20/15 | 246 |
| 11/16/14 | 86001741 | 7/27/15 | 245 |
| 11/9/14 | 86001741 | 7/27/15 | 245 |
| 11/23/14 | 86001741 | 7/27/15 | 245 |
| 11/23/14 | 86001741 | 8/3/15 | 99 |
| 11/16/14 | 86001741 | 8/3/15 | 99 |
| 11/9/14 | 86001741 | 8/3/15 | 99 |
| 11/23/14 | 86001741 | 8/10/15 | 99 |
| 11/16/14 | 86001741 | 8/10/15 | 99 |
| 11/9/14 | 86001741 | 8/10/15 | 99 |
| 11/16/14 | 86001741 | 8/17/15 | 109 |
| 11/9/14 | 86001741 | 8/17/15 | 109 |
| 11/23/14 | 86001741 | 8/17/15 | 109 |
| 11/23/14 | 86001741 | 8/24/15 | 109 |
| 11/16/14 | 86001741 | 8/24/15 | 109 |
| 11/9/14 | 86001741 | 8/24/15 | 109 |
| 11/9/14 | 86001741 | 8/31/15 | 109 |
| 11/23/14 | 86001741 | 8/31/15 | 109 |
| 11/16/14 | 86001741 | 8/31/15 | 109 |
| 11/23/14 | 86001741 | 9/7/15 | 281 |
| 11/9/14 | 86001741 | 9/7/15 | 281 |
| 11/16/14 | 86001741 | 9/7/15 | 281 |
| 11/9/14 | 86001741 | 9/14/15 | 280 |
| 11/23/14 | 86001741 | 9/14/15 | 280 |
| 11/16/14 | 86001741 | 9/14/15 | 280 |
| 11/16/14 | 86001741 | 9/21/15 | 281 |
| 11/9/14 | 86001741 | 9/21/15 | 281 |
| 11/23/14 | 86001741 | 9/21/15 | 281 |
| 11/23/14 | 86001741 | 9/28/15 | 280 |
| 11/16/14 | 86001741 | 9/28/15 | 280 |
| 11/9/14 | 86001741 | 9/28/15 | 280 |
| 11/16/14 | 86001741 | 10/5/15 | 281 |
| 11/9/14 | 86001741 | 10/5/15 | 281 |
| 11/23/14 | 86001741 | 10/5/15 | 281 |
| 11/16/14 | 86001741 | 10/12/15 | 273 |
| 11/9/14 | 86001741 | 10/12/15 | 273 |
| 11/23/14 | 86001741 | 10/12/15 | 273 |
| 11/16/14 | 86001741 | 10/19/15 | 274 |
| 11/9/14 | 86001741 | 10/19/15 | 274 |
| 11/23/14 | 86001741 | 10/19/15 | 274 |
| 11/23/14 | 86001741 | 10/26/15 | 273 |
| 11/9/14 | 86001741 | 10/26/15 | 273 |
| 11/16/14 | 86001741 | 10/26/15 | 273 |
| 11/23/14 | 86001741 | 11/2/15 | 113 |
| 11/9/14 | 86001741 | 11/2/15 | 113 |
| 11/16/14 | 86001741 | 11/2/15 | 113 |
| 11/23/14 | 86001741 | 11/9/15 | 112 |
| 11/23/14 | 86001741 | 11/16/15 | 109 |
| 11/23/14 | 86001741 | 11/23/15 | 108 |
| 11/23/14 | 86001741 | 11/30/15 | 109 |
| 11/16/14 | 86001741 | 12/14/15 | 438 |
| 11/9/14 | 86001741 | 12/14/15 | 438 |
+----------+-----------+---------------------+------+