山东省住房和城乡建设厅定额站子网站,深圳网站 制作信科便宜,成都网站营销,微网站功能mysql 中! 到底走不走索引#xff1f; 很多人疑惑! 到底走不走索引#xff0c; 这里可以肯定的说该操作是可以走索引的#xff0c;但实际情况中都为啥都不走索引呢#xff1f; 首先我们要知道走索引与数据量和数据趋势#xff08;cardinality#xff09;有很大的关系 到底走不走索引 很多人疑惑! 到底走不走索引 这里可以肯定的说该操作是可以走索引的但实际情况中都为啥都不走索引呢 首先我们要知道走索引与数据量和数据趋势cardinality有很大的关系如果表本身就上百条记录那走索引和表扫描区别不大甚至在存在书签跳转情况下还不如表扫描更有效率这个时候可能是不走索引的另外 !操作后获取的结果集在总结果集中占据的比例也是关键因素如果返回的结果集过大大于20%那么可能也不会走索引而是选择更有效率的表扫描了。 我们来看看个例子
CREATE TABLE b (id int(11) NOT NULL AUTO_INCREMENT,age bigint(20) DEFAULT 50,name varchar(50) DEFAULT NULL,PRIMARY KEY (id),KEY name (name)
) ENGINEInnoDBinsert into b (name) values(a),(b),(c),(d),(e),(f),(g),(h),(i);
--多次执行
insert into b (name)
select k from b ;select name, count(*)
from b
group by name explain
select * From b where name !k; explain
select * From b where name !a; 很明显 我们从统计中看到 K的数值很大所以我们!k的数据集才8条在总数据中占比很小可以很好的走索引而如果将k替换成 a则不会走索引变成了全表扫描 MYSQL系列书籍
高可用mysql: https://url41.ctfile.com/f/49289241-959127723-de4738?p2651 (访问密码: 2651)
MySQL王者晋级之路.pdf: https://url41.ctfile.com/f/49289241-959127432-204284?p2651 (访问密码: 2651)
MySQL技术内幕InnoDB存储引擎第2版.pdf: https://url41.ctfile.com/f/49289241-959126379-4590a8?p2651 (访问密码: 2651)
MySQL技术内幕 第4版.pdf: https://url41.ctfile.com/f/49289241-959125506-a5bcec?p2651 (访问密码: 2651)
MySQL管理之道性能调优高可用与监控第二版.pdf: https://url41.ctfile.com/f/49289241-959124249-d59f54?p2651 (访问密码: 2651)
深入浅出MySQL数据库开发、优化与管理维护第2版.pdf: https://url41.ctfile.com/f/49289241-961464090-68bf10?p2651 (访问密码: 2651)
高性能MySQL.第3版.Baron Schwartz.pdf: https://url41.ctfile.com/f/49289241-961462308-52cc5d?p2651 (访问密码: 2651)
MYSQL内核INNODB存储引擎 卷1.pdf: https://url41.ctfile.com/f/49289241-961461357-ee63e3?p2651 (访问密码: 2651)
MySQL技术内幕InnoDB存储引擎第2版.pdf: https://url41.ctfile.com/f/49289241-959126379-4590a8?p2651 (访问密码: 2651)
MySQLDBA修炼之道.pdf: https://url41.ctfile.com/f/49289241-961459500-9b201d?p2651 (访问密码: 2651)
MySQL5.7从入门到精通.pdf: https://url41.ctfile.com/f/49289241-961459329-48cbcf?p2651 (访问密码: 2651)
高可用mysql.pdf: https://url41.ctfile.com/f/49289241-959127723-de4738?p2651 (访问密码: 2651)
HIVE电子书
Practical Hive.pdf: https://url41.ctfile.com/f/49289241-959129883-d35ee9?p2651 (访问密码: 2651)
Hive-Succinctly.pdf: https://url41.ctfile.com/f/49289241-959129709-30f30b?p2651 (访问密码: 2651)
Apache Hive Essentials.pdf: https://url41.ctfile.com/f/49289241-959129691-b1a4aa?p2651 (访问密码: 2651)
Apache Hive Cookbook.pdf: https://url41.ctfile.com/f/49289241-959129619-3a8ea6?p2651 (访问密码: 2651)
hadoop电子书
Practical Hadoop Migration.pdf: https://url41.ctfile.com/f/49289241-959131470-dd3e24?p2651 (访问密码: 2651)
Hadoop实战-陆嘉恒(高清完整版).pdf: https://url41.ctfile.com/f/49289241-959131365-433ec9?p2651 (访问密码: 2651)
Hadoop Spark大数据开发实战.pdf: https://url41.ctfile.com/f/49289241-959131032-ba40ea?p2651 (访问密码: 2651)
Expert Hadoop Administration.pdf: https://url41.ctfile.com/f/49289241-959130468-ba70cd?p2651 (访问密码: 2651)
Big Data Forensics - Learning Hadoop Investigations.pdf: https://url41.ctfile.com/f/49289241-959130435-9ab981?p2651 (访问密码: 2651)
python电子书
python学习手册.pdf: https://url41.ctfile.com/f/49289241-959129403-5b45b1?p2651 (访问密码: 2651)
Python基础教程-第3版.pdf: https://url41.ctfile.com/f/49289241-959128707-de6ef2?p2651 (访问密码: 2651)
Python编程从入门到实践.pdf: https://url41.ctfile.com/f/49289241-959128548-ce965d?p2651 (访问密码: 2651)
Python Projects for Beginners.pdf: https://url41.ctfile.com/f/49289241-959128461-b53321?p2651 (访问密码: 2651)
kafka电子书
Learning Apache Kafka, 2nd Edition.pdf: https://url41.ctfile.com/f/49289241-959134953-a14305?p2651 (访问密码: 2651)
Kafka权威指南.pdf: https://url41.ctfile.com/f/49289241-959134932-295734?p2651 (访问密码: 2651)
Kafka in Action.pdf: https://url41.ctfile.com/f/49289241-959134116-12111a?p2651 (访问密码: 2651)
Apache Kafka实战.pdf: https://url41.ctfile.com/f/49289241-959133999-76ef77?p2651 (访问密码: 2651)
Apache Kafka Cookbook.pdf: https://url41.ctfile.com/f/49289241-959132547-055c36?p2651 (访问密码: 2651)
spark电子书
Spark最佳实践.pdf: https://url41.ctfile.com/f/49289241-959415393-5829fe?p2651 (访问密码: 2651)
数据算法--Hadoop-Spark大数据处理技巧.pdf: https://url41.ctfile.com/f/49289241-959415927-5bdddc?p2651 (访问密码: 2651)
Spark大数据分析实战.pdf: https://url41.ctfile.com/f/49289241-959416377-924161?p2651 (访问密码: 2651)
Spark 2.0 for Beginners.pdf: https://url41.ctfile.com/f/49289241-959416710-7ea156?p2651 (访问密码: 2651)
Pro Spark Streaming.pdf: https://url41.ctfile.com/f/49289241-959416866-6116d7?p2651 (访问密码: 2651)
Spark in Action.pdf: https://url41.ctfile.com/f/49289241-959416986-e759e9?p2651 (访问密码: 2651)
Learn PySpark.pdf: https://url41.ctfile.com/f/49289241-959417049-ac04a0?p2651 (访问密码: 2651)
Fast Data Processing with Spark.pdf: https://url41.ctfile.com/f/49289241-959417157-8ec3b0?p2651 (访问密码: 2651)
Fast Data Processing with Spark, 2nd Edition.pdf: https://url41.ctfile.com/f/49289241-959417211-856d08?p2651 (访问密码: 2651)
OReilly.Learning.Spark.2015.1.pdf: https://url41.ctfile.com/f/49289241-959417292-90c1bc?p2651 (访问密码: 2651)
High Performance Spark.pdf: https://url41.ctfile.com/f/49289241-959417439-7e7893?p2651 (访问密码: 2651)
Machine Learning with PySpark.pdf: https://url41.ctfile.com/f/49289241-959417580-5941b3?p2651 (访问密码: 2651)
Spark for Python Developers.pdf: https://url41.ctfile.com/f/49289241-959417721-d59fbe?p2651 (访问密码: 2651)
Spark Cookbook.pdf: https://url41.ctfile.com/f/49289241-959417811-19c75d?p2651 (访问密码: 2651)
Big Data Analytics with Spark.pdf: https://url41.ctfile.com/f/49289241-959417907-41dbce?p2651 (访问密码: 2651)
PySpark SQL Recipes.pdf: https://url41.ctfile.com/f/49289241-959417970-c23242?p2651 (访问密码: 2651)
Advanced Analytics with Spark Patterns for Learning from Data at Scale .pdf: https://url41.ctfile.com/f/49289241-959417997-a5e3f5?p2651 (访问密码: 2651)
OReilly.Advanced.Analytics.with.Spark.Patterns.for.Learning.from.Data.at.Scale.pdf: https://url41.ctfile.com/f/49289241-959418024-2ff34c?p2651 (访问密码: 2651)
Big Data Analytics Beyond Hadoop_ Real-Time Applications with Storm, Spark, and More Hadoop Alternatives.pdf: https://url41.ctfile.com/f/49289241-959418042-581fb9?p2651 (访问密码: 2651)
