MySQL:Specified key was too long; max key length is 767 bytes
2013-11-19 15:50
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下面的SQL语句
即便是改为
依然是这个错误!!
将mysql数据库脚本中的unique index字段从原来的varchar(256)改成varchar(1024),再次执行报错:
以前写过一篇文章,也是关于这个问题的
在该文中,我经过试验,发现如果将varchar类型的unique index/key设置成最大383,就不会出现问题了。
其实这个问题还有一个解,那就是指定索引的长度:
那么在不改变字段长度的情况下,通过指定索引长度为一个较小的值,就可以避免出现这个问题了。
又如,
此处展示的语句用于创建一个索引,索引使用列名称的前10个字符。
因为多数名称的前10个字符通常不同,所以此索引不会比使用列的全名创建的索引速度慢很多。
CREATE TABLE subscription ( subscriptionid varchar(767) NOT NULL PRIMARY KEY, params blob, dest varchar(1023), sched blob, trigg varchar(1023), initialrecordingtime timestamp, exportifempty boolean, queryname varchar(1023), lastexecuted timestamp );
即便是改为
CREATE TABLE subscription ( subscriptionid varchar(767) NOT NULL PRIMARY KEY, params blob, dest varchar(767), sched blob, trigg varchar(767), initialrecordingtime timestamp, exportifempty boolean, queryname varchar(767), lastexecuted timestamp );
依然是这个错误!!
将mysql数据库脚本中的unique index字段从原来的varchar(256)改成varchar(1024),再次执行报错:
ERROR 1071 (42000) at line 482 in file: 'db/sm1.sql': Specified key was too long; max key length is 767 bytes
以前写过一篇文章,也是关于这个问题的
其实这个问题还有一个解,那就是指定索引的长度:
对于CHAR和VARCHAR列,只用一列的一部分就可创建索引。创建索引时,使用col_name(length)语法,对前缀编制索引。前缀包括每列值的前length个字符。BLOB和TEXT列也可以编制索引,但是必须给出前缀长度。
那么在不改变字段长度的情况下,通过指定索引长度为一个较小的值,就可以避免出现这个问题了。
UNIQUE INDEX (content(32)),
又如,
此处展示的语句用于创建一个索引,索引使用列名称的前10个字符。
CREATE INDEX part_of_name ON customer (name(10));
因为多数名称的前10个字符通常不同,所以此索引不会比使用列的全名创建的索引速度慢很多。
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