创建一张表,其中有个varchar 大字段,并且在这个字段上建索引,结果发现MySQL报错:
ERROR 1709 (HY000): Index column size too large. The maximum column size is 767 bytes.
create table piratebay(
SYS_ID int ,
FILE_NAME VARCHAR(200),
FILE_ID VARCHAR(30),
NUM1 VARCHAR(30),
NUM2 VARCHAR(30),
MAGNET_LINK VARCHAR(500),
PRIMARY KEY (sys_id),
KEY piratebay_n1 (FILE_NAME))
engine=innodb;
Server version: 5.6.28-log MySQL Community Server (GPL)
Server characterset: utf8mb4
Db characterset: utf8mb4
解决办法:
(1)查看相关配置并作出如下设置
innodb_large_prefix = ON
innodb_file_format = Barracuda
innodb_file_per_table = ON
(2)修改建表语句,加入 row_format=DYNAMIC
create table piratebay(
SYS_ID int ,
FILE_NAME VARCHAR(200),
FILE_ID VARCHAR(30),
NUM1 VARCHAR(30),
NUM2 VARCHAR(30),
MAGNET_LINK VARCHAR(500),
PRIMARY KEY (sys_id),
KEY piratebay_n1 (FILE_NAME))
engine=innodb row_format=dynamic;
原因:
MySQL 索引只支持767个字节,utf8mb4 每个字符占用4个字节,所以索引最大长度只能为191个字符,即varchar(191),若想要使用更大的字段,mysql需要设置成支持数据压缩,并且修改表属性 row_format ={DYNAMIC|COMPRESSED}
官方解释:
https://dev.mysql.com/doc/refman/5.5/en/innodb-parameters.html#sysvar_innodb_large_prefix