我有一个表tbl\u sc\u 3\u 4\u ps，其结构如下（id\u team的多个条目可以在一分钟内完成！！！）：

+--------+---------+--------+----------+------+---------------------+
| id     | id_team | bill_n | bill_min | ps   | c_minute            |
+--------+---------+--------+----------+------+---------------------+
| 175019 | team1   | 0.0489 |     NULL | NULL | 2018-08-07 00:00:00 |
| 175020 | team1   | 0.0500 |     NULL | NULL | 2018-08-07 00:01:00 |
| 175021 | team1   | 0.0464 |     NULL | NULL | 2018-08-07 00:02:00 |
| 175022 | team1   | 0.0392 |     NULL | NULL | 2018-08-07 00:03:00 |
| 175023 | team1   | 0.0504 |     NULL | NULL | 2018-08-07 00:04:00 |
| 175024 | team1   | 0.0484 |     NULL | NULL | 2018-08-07 00:05:00 |
| 175025 | team1   | 0.0475 |     NULL | NULL | 2018-08-07 00:06:00 |
| 175026 | team1   | 0.0500 |     NULL | NULL | 2018-08-07 00:07:00 |
| 175027 | team1   | 0.0453 |     NULL | NULL | 2018-08-07 00:08:00 |
| 175028 | team1   | 0.0445 |     NULL | NULL | 2018-08-07 00:09:00 |
+--------+---------+--------+----------+------+---------------------+

并想从tbl\u sc\u 3\u 4\u bill\u min更新bill\u min列（一个c\u min只能有一个bill\u min，c\u min是pkey）：

+---------------------+----------+
| c_minute            | bill_min |
+---------------------+----------+
| 2018-08-07 00:00:00 |   0.0418 |
| 2018-08-07 00:01:00 |   0.0766 |
| 2018-08-07 00:02:00 |   0.1188 |
| 2018-08-07 00:03:00 |   0.1556 |
| 2018-08-07 00:04:00 |   0.2002 |
| 2018-08-07 00:05:00 |   0.2416 |
| 2018-08-07 00:06:00 |   0.2779 |
| 2018-08-07 00:07:00 |   0.3187 |
| 2018-08-07 00:08:00 |   0.3614 |
| 2018-08-07 00:09:00 |   0.4000 |
+---------------------+----------+

我的sql语句：

update dbsdme.tbl_su_3_4_ps as a
inner join dbsdme.tbl_sc_3_4_bill_min as b on b.c_minute = a.c_minute
set a.bill_min = b.bill_min
where a.bill_min is NULL;

这不仅更新bill\u min列，还更新c\u min列（执行查询时带有时间戳）：

+--------+---------+--------+----------+------+---------------------+
| id     | id_team | bill_n | bill_min | ps   | c_minute            |
+--------+---------+--------+----------+------+---------------------+
| 175019 | team1   | 0.0489 |   0.0418 | NULL | 2018-08-12 10:29:31 |
| 175020 | team1   | 0.0500 |   0.0766 | NULL | 2018-08-12 10:29:31 |
| 175021 | team1   | 0.0464 |   0.1188 | NULL | 2018-08-12 10:29:31 |
| 175022 | team1   | 0.0392 |   0.1556 | NULL | 2018-08-12 10:29:31 |
| 175023 | team1   | 0.0504 |   0.2002 | NULL | 2018-08-12 10:29:31 |
| 175024 | team1   | 0.0484 |   0.2416 | NULL | 2018-08-12 10:29:31 |
| 175025 | team1   | 0.0475 |   0.2779 | NULL | 2018-08-12 10:29:31 |
| 175026 | team1   | 0.0500 |   0.3187 | NULL | 2018-08-12 10:29:31 |
| 175027 | team1   | 0.0453 |   0.3614 | NULL | 2018-08-12 10:29:31 |
| 175028 | team1   | 0.0445 |   0.4000 | NULL | 2018-08-12 10:29:31 |
+--------+---------+--------+----------+------+---------------------+

有人知道为什么c\分钟栏也会更新吗？我只想更新一下bill琰min。
致以最诚挚的问候
简