mysql regex_replace:如何在替换中使用regex组

有一张桌子:

| id |      Name       |
|----------------------|
| 1  |test1 test1 test1|
| 2  |test2 test2 test2|

想选择第一个正则表达式组(使用第一个单词来简化)，所以我的查询是:

Want to select 1st regex group (used 1st word to simplify), so my query:

SELECT regexp_replace(name, "^([[:alnum:]]+)[[:space:]].*$","$1") FROM table;

结果:

|test1      |
|test1test2 |

那么结果如何累积呢?以及如何避免它并仍然可以使用正则表达式组?

So how it comes that result is accumulated? And how to avoid it and still be able to use regex group?

UPD : Mysql版本:8.0.11，MySQL社区服务器-GPL

UPD: Mysql version: 8.0.11, MySQL Community Server - GPL