mysql替换字段里数据内容部分字符串

mysql替换表的字段里面内容，如例子：

mysql> select host,user from user  where user=‘testuser‘; 
+-----------------------+----------+
| host                  | user     |
+-----------------------+----------+
| localhost.localdomain | testuser | 
+-----------------------+----------+

update字段host的内容，把"main"改成"slave",用REPLACE

mysql> update user set host=REPLACE(host,‘main‘,‘slave‘) where user=‘testuser‘;       
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select host,user from user  where user=‘testuser‘;                             
+------------------------+----------+
| host                   | user     |
+------------------------+----------+
| localhost.localdoslave | testuser | 
+------------------------+----------+

由查询结果到，数据已经更新成功