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Author: simuleite

ComputerScience/基本操作/mysql使用/index.html

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@@ -143,7 +143,7 @@
       <div class="sidebar-panel-container">
         <!--noindex-->
         <div class="post-toc-wrap sidebar-panel">
-            <div class="post-toc animated"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#%E7%B4%A2%E5%BC%95%E5%8E%9F%E7%90%86"><span class="nav-text"> 索引原理</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%BC%95%E6%93%8E"><span class="nav-text"> 引擎</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E4%B8%BA%E4%BB%80%E4%B9%88innodb%E5%BB%BA%E8%AE%AE%E6%AF%8F%E5%BC%A0%E8%A1%A8%E5%BF%85%E9%A1%BB%E5%BB%BA%E7%AB%8B%E4%B8%BB%E9%94%AE%E5%B9%B6%E7%94%A8%E8%87%AA%E5%A2%9E%E6%95%B4%E5%9E%8B"><span class="nav-text"> 为什么InnoDB建议每张表必须建立主键，并用自增整型？</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#b%E6%A0%91%E5%A6%82%E4%BD%95%E6%94%AF%E6%8C%81%E8%8C%83%E5%9B%B4%E6%9F%A5%E8%AF%A2"><span class="nav-text"> B+树如何支持范围查询</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E8%81%94%E5%90%88%E4%B8%BB%E9%94%AE%E7%B4%A2%E5%BC%95%E4%B8%BA%E4%BB%80%E4%B9%88%E6%98%AF%E6%9C%80%E5%B7%A6%E5%89%8D%E7%BC%80%E5%8E%9F%E5%88%99"><span class="nav-text"> 联合主键索引，为什么是最左前缀原则？</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E4%BA%8B%E5%8A%A1"><span class="nav-text"> 事务</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%8E%9F%E5%AD%90%E6%80%A7-atomicity"><span class="nav-text"> 原子性 Atomicity</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E4%B8%80%E8%87%B4%E6%80%A7-consistency"><span class="nav-text"> 一致性 Consistency</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E9%9A%94%E7%A6%BB%E6%80%A7-isolation"><span class="nav-text"> 隔离性 Isolation</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E6%8C%81%E4%B9%85%E6%80%A7-durability"><span class="nav-text"> 持久性 Durability</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E4%BD%BF%E7%94%A8"><span class="nav-text"> 使用</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%90%AF%E5%8A%A8%E6%95%B0%E6%8D%AE%E5%BA%93"><span class="nav-text"> 启动数据库</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E7%99%BB%E5%BD%95%E6%95%B0%E6%8D%AE%E5%BA%93"><span class="nav-text"> 登录数据库</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%AF%BC%E5%85%A5%E6%95%B0%E6%8D%AE%E5%BA%93"><span class="nav-text"> 导入数据库</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E6%95%B0%E6%8D%AE%E5%BA%93"><span class="nav-text"> 数据库</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E8%A1%A8"><span class="nav-text"> 表</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E6%9F%A5%E8%AF%A2"><span class="nav-text"> 查询</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E6%8E%92%E5%BA%8F"><span class="nav-text"> 排序</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E7%AD%9B%E9%80%89"><span class="nav-text"> 筛选</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E9%80%BB%E8%BE%91%E6%93%8D%E4%BD%9C%E7%AC%A6"><span class="nav-text"> 逻辑操作符</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E6%8F%92%E5%85%A5"><span class="nav-text"> 插入</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E6%9B%B4%E6%96%B0"><span class="nav-text"> 更新</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E5%88%A0%E9%99%A4"><span class="nav-text"> 删除</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E8%81%94%E7%BB%93"><span class="nav-text"> 联结</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E5%AE%89%E8%A3%85"><span class="nav-text"> 安装</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%8E%8B%E7%BC%A9%E5%8C%85%E5%AE%89%E8%A3%85"><span class="nav-text"> 压缩包安装</span></a></li></ol></li></ol></div>
+            <div class="post-toc animated"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#%E7%B4%A2%E5%BC%95%E5%8E%9F%E7%90%86"><span class="nav-text"> 索引原理</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%BC%95%E6%93%8E"><span class="nav-text"> 引擎</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E4%B8%BA%E4%BB%80%E4%B9%88innodb%E5%BB%BA%E8%AE%AE%E6%AF%8F%E5%BC%A0%E8%A1%A8%E5%BF%85%E9%A1%BB%E5%BB%BA%E7%AB%8B%E4%B8%BB%E9%94%AE%E5%B9%B6%E7%94%A8%E8%87%AA%E5%A2%9E%E6%95%B4%E5%9E%8B"><span class="nav-text"> 为什么InnoDB建议每张表必须建立主键，并用自增整型？</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#b%E6%A0%91%E5%A6%82%E4%BD%95%E6%94%AF%E6%8C%81%E8%8C%83%E5%9B%B4%E6%9F%A5%E8%AF%A2"><span class="nav-text"> B+树如何支持范围查询</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E8%81%94%E5%90%88%E4%B8%BB%E9%94%AE%E7%B4%A2%E5%BC%95%E4%B8%BA%E4%BB%80%E4%B9%88%E6%98%AF%E6%9C%80%E5%B7%A6%E5%89%8D%E7%BC%80%E5%8E%9F%E5%88%99"><span class="nav-text"> 联合主键索引，为什么是最左前缀原则？</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E7%B4%A2%E5%BC%95%E4%BC%98%E5%8C%96%E5%8E%9F%E5%88%99"><span class="nav-text"> 索引优化原则</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#explain%E6%80%A7%E8%83%BD%E5%88%86%E6%9E%90"><span class="nav-text"> explain性能分析</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#%E5%AD%97%E6%AE%B5%E8%A7%A3%E9%87%8A"><span class="nav-text"> 字段解释</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#sql%E8%AF%AD%E5%8F%A5%E4%BC%98%E5%8C%96"><span class="nav-text"> sql语句优化</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E7%BC%93%E5%AD%98"><span class="nav-text"> 缓存</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E4%BA%8B%E5%8A%A1"><span class="nav-text"> 事务</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%8E%9F%E5%AD%90%E6%80%A7-atomicity"><span class="nav-text"> 原子性 Atomicity</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E4%B8%80%E8%87%B4%E6%80%A7-consistency"><span class="nav-text"> 一致性 Consistency</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E9%9A%94%E7%A6%BB%E6%80%A7-isolation"><span class="nav-text"> 隔离性 Isolation</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E6%8C%81%E4%B9%85%E6%80%A7-durability"><span class="nav-text"> 持久性 Durability</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E4%BD%BF%E7%94%A8"><span class="nav-text"> 使用</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%90%AF%E5%8A%A8%E6%95%B0%E6%8D%AE%E5%BA%93"><span class="nav-text"> 启动数据库</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E7%99%BB%E5%BD%95%E6%95%B0%E6%8D%AE%E5%BA%93"><span class="nav-text"> 登录数据库</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%AF%BC%E5%85%A5%E6%95%B0%E6%8D%AE%E5%BA%93"><span class="nav-text"> 导入数据库</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E6%95%B0%E6%8D%AE%E5%BA%93"><span class="nav-text"> 数据库</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E8%A1%A8"><span class="nav-text"> 表</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E6%9F%A5%E8%AF%A2"><span class="nav-text"> 查询</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E6%8E%92%E5%BA%8F"><span class="nav-text"> 排序</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E7%AD%9B%E9%80%89"><span class="nav-text"> 筛选</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E9%80%BB%E8%BE%91%E6%93%8D%E4%BD%9C%E7%AC%A6"><span class="nav-text"> 逻辑操作符</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E6%8F%92%E5%85%A5"><span class="nav-text"> 插入</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E6%9B%B4%E6%96%B0"><span class="nav-text"> 更新</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E5%88%A0%E9%99%A4"><span class="nav-text"> 删除</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E8%81%94%E7%BB%93"><span class="nav-text"> 联结</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#%E5%AE%89%E8%A3%85"><span class="nav-text"> 安装</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#%E5%8E%8B%E7%BC%A9%E5%8C%85%E5%AE%89%E8%A3%85"><span class="nav-text"> 压缩包安装</span></a></li></ol></li></ol></div>
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@@ -225,7 +225,7 @@ <h1 class="post-title" itemprop="name headline">
         <i class="far fa-calendar-check"></i>
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       <span class="post-meta-item-text">更新于</span>
-      <time title="修改时间：2025-02-15 22:07:25" itemprop="dateModified" datetime="2025-02-15T22:07:25+08:00">2025-02-15</time>
+      <time title="修改时间：2025-02-20 20:55:09" itemprop="dateModified" datetime="2025-02-20T20:55:09+08:00">2025-02-20</time>
     </span>
 
 
@@ -256,6 +256,49 @@ <h2 id="联合主键索引为什么是最左前缀原则"><a class="markdownIt-A
 <p>最左前缀原则：不能跳过左边的索引，必须从最左边索引开始，逐步增加条件。<br />
 因为联合主键索引底层的B+树就是按照主键顺序排序的，会从左到右进行比较；如果跳过了左边的主键，那就找不到了，因为第二个主键不一定是排好序的！。<br />
 首先按照第一个主键排序，然后按照第二个主键排序。在同一个主键内，二级主键是有序的，但是跳出这个圈，就是无序的。</p>
+<h1 id="索引优化原则"><a class="markdownIt-Anchor" href="#索引优化原则"></a> 索引优化原则</h1>
+<h2 id="explain性能分析"><a class="markdownIt-Anchor" href="#explain性能分析"></a> explain性能分析</h2>
+<p><code>explain extended</code>: <span class="katex"><span class="katex-mathml"><math><semantics><mrow><mi>r</mi><mi>o</mi><mi>w</mi><mi>s</mi><mo>∗</mo><mi>f</mi><mi>i</mi><mi>l</mi><mi>t</mi><mi>e</mi><mi>r</mi><mi>e</mi><mi>d</mi><mi mathvariant="normal">/</mi><mn>100</mn></mrow><annotation encoding="application/x-tex">rows * filtered/100</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.46528em;vertical-align:0em;"></span><span class="mord mathdefault" style="margin-right:0.02778em;">r</span><span class="mord mathdefault">o</span><span class="mord mathdefault" style="margin-right:0.02691em;">w</span><span class="mord mathdefault">s</span><span class="mspace" style="margin-right:0.2222222222222222em;"></span><span class="mbin">∗</span><span class="mspace" style="margin-right:0.2222222222222222em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathdefault" style="margin-right:0.10764em;">f</span><span class="mord mathdefault">i</span><span class="mord mathdefault" style="margin-right:0.01968em;">l</span><span class="mord mathdefault">t</span><span class="mord mathdefault">e</span><span class="mord mathdefault" style="margin-right:0.02778em;">r</span><span class="mord mathdefault">e</span><span class="mord mathdefault">d</span><span class="mord">/</span><span class="mord">1</span><span class="mord">0</span><span class="mord">0</span></span></span></span>可以估算出将要和explain中前一个表达式进行连接的行数。<br />
+<code>show warning</code>: Mysql的提示信息，可能会帮你优化。</p>
+<h3 id="字段解释"><a class="markdownIt-Anchor" href="#字段解释"></a> 字段解释</h3>
+<p>select_type</p>
+<ul>
+<li>Primary 最外层的select。</li>
+<li>Subquery 不在from语句中，包含在select中的子查询。</li>
+<li>Derived 包含在from语句中的子查询。派生表。<br />
+id</li>
+<li>表示执行顺序，顺序越靠后优先级越高<br />
+<strong>type</strong><br />
+效率优先级 system &gt; const &gt; eq_ref &gt; ref &gt; range &gt; index &gt; ALL</li>
+</ul>
+<blockquote>
+<p>一般来说range是及格线，最好达到ref</p>
+</blockquote>
+<ul>
+<li>NULL mysql通过优化和底层原理，不访问表或索引就取到值。如求最小值，通过B+树直接拿到。</li>
+<li>system, const system是const的特例，const表示常量查询。表只有一行，为const查询。只有一条元组匹配，为system查询。</li>
+<li>eq_ref 主键关联查询，表有几行。</li>
+<li>ref 使用非主键（不唯一）索引，表有很多行。使用普通索引或唯一索引的部分前缀。</li>
+<li>range 范围查找，包括比较符号。</li>
+<li>index 无查询条件，全选。扫描全索引就能拿到结果，一般扫描二级索引（Mysql优先选择同等条件下更小的索引）。</li>
+<li>ALL 全表扫描。扫描聚集索引，比index更大</li>
+</ul>
+<h2 id="sql语句优化"><a class="markdownIt-Anchor" href="#sql语句优化"></a> sql语句优化</h2>
+<ul>
+<li>尽量使用覆盖索引</li>
+</ul>
+<figure class="highlight sql"><table><tr><td class="code"><pre><span class="line"><span class="comment">-- 推荐，其中name和age都有索引</span></span><br><span class="line"><span class="keyword">select</span> name, age <span class="keyword">from</span> your_table <span class="keyword">where</span> <span class="keyword">condition</span></span><br><span class="line"><span class="comment">-- 不推荐</span></span><br><span class="line"><span class="keyword">select</span> <span class="operator">*</span> <span class="keyword">from</span> your_table <span class="keyword">where</span> <span class="keyword">condition</span></span><br></pre></td></tr></table></figure>
+<ul>
+<li>少用or或in；不对索引用函数；不让索引发生隐式转换</li>
+<li>减少搜索范围；范围过大，mysql会认为全表扫描更快，从而不走索引</li>
+<li><code>force index(your_index)</code> 强制索引（注意，不一定更快！可能更多回表）</li>
+<li>试试用<code>like</code>代替范围查询</li>
+</ul>
+<h1 id="缓存"><a class="markdownIt-Anchor" href="#缓存"></a> 缓存</h1>
+<p>Mysql8以后移除了缓存。</p>
+<blockquote>
+<p>Mysql缓存的本质是KV Map。然而，对于高频修改的数据，Map缓存下来的是<strong>脏数据</strong>，因此不实用。</p>
+</blockquote>
 <h1 id="事务"><a class="markdownIt-Anchor" href="#事务"></a> 事务</h1>
 <h2 id="原子性-atomicity"><a class="markdownIt-Anchor" href="#原子性-atomicity"></a> 原子性 Atomicity</h2>
 <figure class="highlight sql"><table><tr><td class="code"><pre><span class="line">BUSINESS</span><br><span class="line"><span class="keyword">sql</span>语句<span class="number">1</span></span><br><span class="line"><span class="keyword">sql</span>语句<span class="number">2</span></span><br><span class="line"><span class="keyword">COMMIT</span></span><br></pre></td></tr></table></figure>