Mysql如何将数据从一个字段复制到同一个表中的其他字段

Question

我有mysql表如下：

    id      host             url
--------------------------------------
    1                   test.com/index.php
    2                   domain.com/list
    3                   www.stackoverflow.com/questions/ask

我需要输出如下

    id      host                 url
------------------------------------------
    1     test.com             test.com/index.php
    2     domain.com           domain.com/list
    3     stackoverflow.com    www.stackoverflow.com/questions/ask

提前致谢。

Answer 1

使用SUBSTRING_INDEX(str, delim, count)：

UPDATE tablename
SET host = SUBSTRING_INDEX(url, '/', 1);

SQL Fiddle Demo

这会使你的表看起来像：

| ID |                  HOST |                                 URL |
--------------------------------------------------------------------
|  1 |              test.com |                  test.com/index.php |
|  2 |            domain.com |                     domain.com/list |
|  3 | www.stackoverflow.com | www.stackoverflow.com/questions/ask |

Answer 2

假设您的表名为t：

UPDATE t
SET host=SUBSTRING_INDEX(url, '/', 1);

Answer 3

使用SUBSTRING_INDEX

UPDATE tbl1 SET host = SUBSTRING_INDEX(url, '/', 1)