MySQL索引(一)

数据库开发中索引的使用占了很重要的位置，好的索引会使数据库的读写效率加倍，烂的索引则会拖累整个系统甚至引发灾难。

索引分三类：

index ----普通的索引,数据可以重复

unique ----唯一索引,唯一索引,要求所有记录都唯一

primary key ----主键索引,也就是在唯一索引的基础上相应的列必须为主键

一般的创建索引的语句如下：

?

</p><p><br>EXPLAIN SELECT *<br>FROM tb_test<br>WHERE fval LIKE '%ab';</p><p><img style="max-width: 100%;height: auto;width: auto\9;" src="//img.reader8.net/uploadfile/jiaocheng/20140149/2836/2014012803362442451.gif" alt="MySQL目录(一)"></p> </p></div><div style="margin:0 auto;width:300px;height:250px;position:relative;"> <script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <!-- 移动端全站正文 --> <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-6147101717324856" data-ad-slot="1958144088" data-ad-format="auto"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script></div> <div class="subn-nav"><a href="//m.reader8.net">读书人网</a> ><a href="//m.reader8.net/jiaocheng/mysql/">Mysql</a></div><div class="sp-jctu"><h3><span> 热点推荐 </span></h3><ul><li><p><a href="//m.reader8.net/jiaocheng/20140428/2316719.html">mysql 5.6中sql语句统计每个目录的具体</a></p></li> <li><p><a href="//m.reader8.net/jiaocheng/20140427/2315827.html">MySQL删除重复数据行只保存一条</a></p></li> <li><p><a href="//m.reader8.net/jiaocheng/20140426/2314905.html">Mysql容易存储过程入门示例与Java调用</a></p></li> <li><p><a href="//m.reader8.net/jiaocheng/20140426/2314904.html">MySQL双主机双Master提案测试</a></p></li> <li><p><a href="//m.reader8.net/jiaocheng/20140425/2313854.html">MySQL增添数据文件</a></p></li> <li><p><a href="//m.reader8.net/jiaocheng/20140425/2313853.html">MySQL截取字符串函数步骤</a></p></li> <li><p><a href="//m.reader8.net/jiaocheng/20140423/2312002.html">绿色mysql下载地址</a></p></li> <li><p><a href="//m.reader8.net/jiaocheng/20140422/2310706.html">mysql设立访问权限</a></p></li> <li><p><a href="//m.reader8.net/jiaocheng/20140422/2310705.html">从Oracle迁移到Mysql事先必须知道的50</a></p></li> <li><p><a href="//m.reader8.net/jiaocheng/20140421/2309609.html">Mysql主从形式搭建</a></p></li> </ul></div><div style="display:none;"> <script> var _hmt = _hmt || []; (function() { var hm = document.createElement("script"); hm.src = "//hm.baidu.com/hm.js?d6151f323a57d16696165e47eee86d53"; var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(hm, s); })(); </script></div> <div class="footer"><p>触屏版 | <a href="//www.reader8.net/jiaocheng/20120924/1841584.html#fromapp">电脑版</a></p><p>读书人网 m.reader8.net</p></div> <script language="javascript"> function clickme(sad){ var divobjdiv = document.getElementById("divobjdiv" + sad); if(divobjdiv.style.display =="none"){ divobjdiv.style.display ="block"; }else{ divobjdiv.style.display ="none"; } var wenzi = document.getElementById('divobjimg' + sad); if(wenzi.innerText == "收起"){ wenzi.innerText = "查看更多"; }else{ wenzi.innerText = "收起"; } } </script> <div id="back-top"><a href="#top"><span></span></a></div> </body> </html>