root@test 07:57:52>alter table article drop index ind_article_url;Query OK, 144384 rows affected (16.29 sec)Records: 144384 Duplicates: 0 Warnings: 0root@test 07:58:40>alter table article add index ind_article_url(url);Query OK, 144384 rows affected, 1 warning (19.52 sec)Records: 144384 Duplicates: 0 Warnings: 0root@test 07:59:23>show warnings;+―――+――+―――――――――――――――――――+| Level  | Code | Message                         |+―――+――+―――――――――――――――――――+| Warning | 1071 | Specified key was too long; max key length is 767 bytes |+―――+――+―――――――――――――――――――+1 row in set (0.00 sec)

`URL` varchar(512) default NULL COMMENT ‘外鏈url',……KEY `ind_article_url` (`URL`(383))…..DEFAULT CHARSET=gbk……drop table test;create table test(test varchar(767) primary key)charset=latin5;