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	<title>MySQL - 四号程序员</title>
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		<title>MySQL 8性能低(于5.7)原因排查</title>
		<link>https://www.coder4.com/archives/7596</link>
					<comments>https://www.coder4.com/archives/7596#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Tue, 14 Dec 2021 09:37:41 +0000</pubDate>
				<category><![CDATA[Linux]]></category>
		<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[5.7]]></category>
		<category><![CDATA[8]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[性能差]]></category>
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					<description><![CDATA[在前文 《阿里云自建MySQL的性能测试(多配置对比)》中，我们发现MySQL 8比MySQL5.7的性能低了33%，今天有空，重新探索了下原因(然而并没有彻底解决）。 1 默认参数差异 根据查阅资料，两者主要有以下默认参数差异： have_query_cache，8中cache被干没了 bin-log，8开启，5.7没开启 innodb_flush_neighbors，8关闭，5.7开启 2 实验1：5.7关闭cache mysql -pmysql123 -e[......] 继续阅读]]></description>
		
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		<title>阿里云自建MySQL的性能测试(多配置对比)</title>
		<link>https://www.coder4.com/archives/7473</link>
					<comments>https://www.coder4.com/archives/7473#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Thu, 02 Dec 2021 10:25:39 +0000</pubDate>
				<category><![CDATA[Linux]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[压测]]></category>
		<category><![CDATA[性能测试]]></category>
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					<description><![CDATA[本文测试下在阿里云上自建MySQL的性能，主要测试工具sysbench，虚拟机环境：阿里云 1 MySQL启动脚本 服务器配置：4核8G，PL0磁盘，ecs.g6.xlarge 为了方便切换版本和重现，我们使用Docker部署，先安装并启用docker： yum install -y docker service docker start 脚本如下： #!/bin/bash NAME="mysql" PUID="1000" PGID="1000" VOLUME=[......] 继续阅读]]></description>
		
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		<title>Spring Boot配置Datasource适配utf8mb4</title>
		<link>https://www.coder4.com/archives/7091</link>
					<comments>https://www.coder4.com/archives/7091#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Fri, 23 Oct 2020 07:44:04 +0000</pubDate>
				<category><![CDATA[Java]]></category>
		<category><![CDATA[emoji]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[utf8mb4]]></category>
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					<description><![CDATA[由于MySQL设计的编码不合理，默认utf8是不能存储emoji表情的，会报错。 1 修改MySQL表的数据集 alter table tbl_xxx character set utf8mb4; 2 修改yaml配置 datasource: tomcat: initSQL: SET NAMES utf8mb4 url: jdbc:mysql://xxxxxx-writer:3306/xxxx?Unicode=true&#38;character[......] 继续阅读]]></description>
		
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		<title>MySQL添加唯一索引前去除重复数据</title>
		<link>https://www.coder4.com/archives/7025</link>
					<comments>https://www.coder4.com/archives/7025#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Wed, 03 Jun 2020 22:18:15 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[去重]]></category>
		<category><![CDATA[唯一索引]]></category>
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					<description><![CDATA[delete from YOUR_TABLE where id not in (select id from (select max(id) as id from YOUR_TABLE group by UNIQUE_FIELD) as b); &#160;[......] 继续阅读]]></description>
		
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		<title>如何将utf8的表转为utf8mb4</title>
		<link>https://www.coder4.com/archives/6091</link>
					<comments>https://www.coder4.com/archives/6091#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Thu, 05 Jul 2018 02:29:09 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[utf8mb4]]></category>
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					<description><![CDATA[ALTER TABLE xxx CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci; &#160;[......] 继续阅读]]></description>
		
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		<title>理解MySQL的四种事务隔离级别</title>
		<link>https://www.coder4.com/archives/5996</link>
					<comments>https://www.coder4.com/archives/5996#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Sun, 25 Mar 2018 08:37:17 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[事物隔离级别]]></category>
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					<description><![CDATA[转载自：《MySQL的四种事务隔离级别》 一、事务的基本要素（ACID） 原子性（Atomicity）：事务开始后所有操作，要么全部做完，要么全部不做，不可能停滞在中间环节。事务执行过程中出错，会回滚到事务开始前的状态，所有的操作就像没有发生一样。也就是说事务是一个不可分割的整体，就像化学中学过的原子，是物质构成的基本单位。 一致性（Consistency）：事务开始前和结束后，数据库的完整性约束没有被破坏 。比如A向B转账，不可能A扣了钱，B却没收到。 隔离性（Is[......] 继续阅读]]></description>
		
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		<title>[转] MySQL 建库 建用户 相关命令</title>
		<link>https://www.coder4.com/archives/4633</link>
					<comments>https://www.coder4.com/archives/4633#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Fri, 26 Jun 2015 02:32:33 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[建库]]></category>
		<category><![CDATA[建用户]]></category>
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					<description><![CDATA[转载自：MYSQL建库建用户命令 1、登陆MySQL:mysql -u root -p password：输入密码 2、查看用户信息select user,host,password from mysql.user;select user,host from mysql.user; 3、设置密码set password for root@localhost=password('在这里填入root密码'); 4、修改密码方法1：mysqladmin -u root -p p[......] 继续阅读]]></description>
		
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		<item>
		<title>Windows下解压缩安装MySQL 5.6</title>
		<link>https://www.coder4.com/archives/4290</link>
					<comments>https://www.coder4.com/archives/4290#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Wed, 17 Sep 2014 15:43:16 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[windows]]></category>
		<category><![CDATA[安装]]></category>
		<category><![CDATA[解压缩]]></category>
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					<description><![CDATA[1、下载 http://cdn.mysql.com/Downloads/MySQL-5.6/mysql-5.6.20-winx64.zip 2、解压缩 3、配置 将my-default.ini复制为my.ini，并修改如下内容： [mysqld] basedir = D:\\soft\\mysql datadir = D:\\soft\\mysql\\data character_set_server=utf8 [client] default-c[......] 继续阅读]]></description>
		
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		<title>MySQL中GROUP_CONCAT中排序</title>
		<link>https://www.coder4.com/archives/4176</link>
					<comments>https://www.coder4.com/archives/4176#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Wed, 09 Apr 2014 03:22:26 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[By]]></category>
		<category><![CDATA[Group]]></category>
		<category><![CDATA[GROUP_CONCAT]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[排序]]></category>
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					<description><![CDATA[原来GROUP_CONCAT中，是支持GROUP内排序的，自己好土。。 SELECT student_name, GROUP_CONCAT(DISTINCT test_score ORDER BY test_score DESC SEPARATOR &#039; &#039;) FROM student GROUP BY student_name;[......] 继续阅读]]></description>
		
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		<title>MySQL中，Group By后，取每组的Top N条记录</title>
		<link>https://www.coder4.com/archives/4171</link>
					<comments>https://www.coder4.com/archives/4171#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Tue, 01 Apr 2014 07:35:11 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[By]]></category>
		<category><![CDATA[Group]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[N]]></category>
		<category><![CDATA[sort]]></category>
		<category><![CDATA[Top]]></category>
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					<description><![CDATA[转载自：http://www.geeklab.info/2012/11/mysql-how-to-get-top-n-rows-for-each-group/ We have the following table and data: &#160; CREATE TEMPORARY TABLE girls( name text, haircolor text, score INT ); INSERT INTO girls VALUES (&#039;M[......] 继续阅读]]></description>
		
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