navicat为mysql建立索引_MySQL
Navicat
bitsCN.com索引的目的是大大提高查询效率,还有读写效率。
kettle向sql里面插入,更新时,也要建立索引,可以大大提升处理时间。
但是建立索引报错:Specified key was too long; max key length is 1000 bytes
这是mysql中,索引字段的类型设置的总体过长,看一下fields里面字段类型,总体加起来不超过1000字节
注意,字段长度,是char长度乘以自身字段类型的位数,累加和不能超过限定的key长1000:
latin1 = 1 byte = 1 character
uft8 = 3 byte = 1 character
gbk = 2 byte = 1 character
以GBK为例:
CREATE UNIQUE INDEX `unique_record` ON reports (`report_name`, `report_client`, `report_city`);
其中report_name varchar(200), report_client varchar(200), report_city varchar(200)
(200 + 200 +200) * 2 = 1200 > 1000,就会报1071错误,只要将report_city改为varchar(100)那么索引就能成功建立。
但如果表是UTF8字符集,那索引还是建立不了,因此要乘以3。
KEY `idx_1` (`packagename`,`storename`,`app_name`,`version`,`category`,`app_link_hash`) USING BTREE
字段类型都是utf8,乘3后,超过1000。
我建的表,字段长度超了,而数据不能动,所以就用了一下小技巧:
1,applink字段要200以上,用了必超。解决办法:将applink用MD5算法,转换为特定长度的applink_hash码(32位长),一一对应,长度特定,用这个新字段只有32位就行了。排除过长字段,转换成特定hashcode,一一对应。
2,kettle插入时分析唯一key。字段之间关系,很多字段联合起来可以唯一确定某个字段,那这个字段就不用出现在索引中。kettle插入时就不用去比对这个字段
3,改成小字段的兼容类型。如果字段内容,允许,也就是包含的内容,很少,比如utf8的类型,可以修改成gbk,就可以省去一个字段。但是数据内容必须能被gbk包含,否则,内容不识别,插进去也没用。
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