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<p>本备忘单旨在快速理解 <a href="https://mysql.com">MySQL</a> 所涉及的主要概念，提供了最常用的SQL语句，供您参考。</p>
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</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist row-span-3"><div class="wrap-header h3wrap"><h3 id="介绍"><a aria-hidden="true" tabindex="-1" href="#介绍"><span class="icon icon-link"></span></a>介绍</h3><div class="wrap-body">
<!--rehype:wrap-class=row-span-3-->
<p>MySQL 为关系型数据库(Relational Database Management System)，一个关系型数据库由一个或数个表格组成，如下所示的一个表格</p>
<hr>
<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line"> name ▼ 键 ▼ 列<span class="token punctuation">(</span>col<span class="token punctuation">)</span>
</span><span class="code-line">┌┈┈┈┈┬┈┈┈┈┈┈┈┈┬┈┈┈┈┈┈┬┈┈┈┈┈┈┈┐
</span><span class="code-line">┆ <span class="token function">id</span> ┆ name ┆ uid ┆ level ┆ ◀ 表头header
</span><span class="code-line">├┈┈┈┈┼┈┈┈┈┈┈┈┈┤┈┈┈┈┈┈┤┈┈┈┈┈┈┈┤
</span><span class="code-line">┆ <span class="token number">1</span> ┆ mysql ┆ <span class="token number">0</span> ┆ <span class="token number">3</span> ┆
</span><span class="code-line">├┈┈┈┈┼┈┈┈┈┈┈┈┈┤┈┈┈┈┈┈┤┈┈┈┈┈┈┈┤
</span><span class="code-line">┆ <span class="token number">2</span> ┆ redis ┆ <span class="token number">12</span> ┆ <span class="token number">1</span> ┆ ◀ 行 row
</span><span class="code-line">└┈┈┈┈┴┈┈┈┈┈┈┈┈┴┈┈┈┈┈┈┴┈┈┈┈┈┈┈┘
</span><span class="code-line"> redis ▲ 值
</span></code></pre>
<hr>
<ul>
<li><code>表头(header)</code> 每一列的名称</li>
<li><code>列(col)</code> 具有相同数据类型的数据的集合</li>
<li><code>行(row)</code> 每一行用来描述某个人/物的具体信息</li>
<li><code>值(value)</code> 行的具体信息，每个值与该列数据类型相同</li>
<li><code>键(key)</code> 用来识别某个特定的人/物的方法，有唯一性</li>
</ul>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="登录mysql"><a aria-hidden="true" tabindex="-1" href="#登录mysql"><span class="icon icon-link"></span></a>登录MySQL</h3><div class="wrap-body">
<pre class="language-shell"><code class="language-shell code-highlight"><span class="code-line"><span class="token comment"># 默认用户名&#x3C;root>，-p 是密码，</span>
</span><span class="code-line"><span class="token comment"># ⚠️参数后面不需要空格</span>
</span><span class="code-line">mysql <span class="token parameter variable">-h</span> <span class="token number">127.0</span>.0.1 <span class="token parameter variable">-u</span> <span class="token operator">&#x3C;</span>用户名<span class="token operator">></span> -p<span class="token operator">&#x3C;</span>密码<span class="token operator">></span>
</span><span class="code-line">mysql <span class="token parameter variable">-D</span> 数据库名 <span class="token parameter variable">-h</span> 主机名 <span class="token parameter variable">-u</span> 用户名 <span class="token parameter variable">-p</span>
</span><span class="code-line">mysql <span class="token parameter variable">-h</span> <span class="token operator">&#x3C;</span>host<span class="token operator">></span> <span class="token parameter variable">-P</span> <span class="token operator">&#x3C;</span>端口号<span class="token operator">></span> <span class="token parameter variable">-u</span> <span class="token operator">&#x3C;</span>user<span class="token operator">></span> <span class="token parameter variable">-p</span> <span class="token punctuation">[</span>db_name<span class="token punctuation">]</span>
</span><span class="code-line">mysql <span class="token parameter variable">-h</span> <span class="token operator">&#x3C;</span>host<span class="token operator">></span> <span class="token parameter variable">-u</span> <span class="token operator">&#x3C;</span>user<span class="token operator">></span> <span class="token parameter variable">-p</span> <span class="token punctuation">[</span>db_name<span class="token punctuation">]</span>
</span></code></pre>
</div></div></div><div class="wrap h3body-exist row-span-3"><div class="wrap-header h3wrap"><h3 id="常用的"><a aria-hidden="true" tabindex="-1" href="#常用的"><span class="icon icon-link"></span></a>常用的</h3><div class="wrap-body">
<!--rehype:wrap-class=row-span-3-->
<h4 id="数据库-database"><a aria-hidden="true" tabindex="-1" href="#数据库-database"><span class="icon icon-link"></span></a>数据库 Database</h4>
<table><thead><tr><th align="left">:-</th><th align="left">:-</th></tr></thead><tbody><tr><td align="left"><code>CREATE DATABASE</code> db <code>;</code></td><td align="left"><code>创建</code>数据库</td></tr><tr><td align="left"><code>SHOW DATABASES;</code></td><td align="left"><code>列出</code>数据库</td></tr><tr><td align="left"><code>USE</code> db<code>;</code></td><td align="left"><code>切换</code>到数据库</td></tr><tr><td align="left"><code>CONNECT</code> db <code>;</code></td><td align="left"><code>切换</code>到数据库</td></tr><tr><td align="left"><code>DROP DATABASE</code> db<code>;</code></td><td align="left"><code>删除</code>数据库</td></tr></tbody></table>
<h4 id="表-table"><a aria-hidden="true" tabindex="-1" href="#表-table"><span class="icon icon-link"></span></a>表 Table</h4>
<table><thead><tr><th align="left">:-</th><th align="left">:-</th></tr></thead><tbody><tr><td align="left"><code>SHOW TABLES;</code></td><td align="left">列出当前数据库的表</td></tr><tr><td align="left"><code>SHOW FIELDS FROM</code> t<code>;</code></td><td align="left">表的列表字段</td></tr><tr><td align="left"><code>DESC</code> t<code>;</code></td><td align="left">显示表格结构</td></tr><tr><td align="left"><code>SHOW CREATE TABLE</code>t<code>;</code></td><td align="left">显示创建表sql</td></tr><tr><td align="left"><code>TRUNCATE TABLE</code>t<code>;</code></td><td align="left">删除表中的所有数据</td></tr><tr><td align="left"><code>DROP TABLE</code>t<code>;</code></td><td align="left">删除表格</td></tr></tbody></table>
<h4 id="proccess"><a aria-hidden="true" tabindex="-1" href="#proccess"><span class="icon icon-link"></span></a>Proccess</h4>
<table><thead><tr><th align="left">:-</th><th align="left">:-</th></tr></thead><tbody><tr><td align="left"><code>show processlist;</code></td><td align="left">列出进程</td></tr><tr><td align="left"><code>kill</code> pid<code>;</code></td><td align="left">杀死进程</td></tr></tbody></table>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="查看-mysql-信息"><a aria-hidden="true" tabindex="-1" href="#查看-mysql-信息"><span class="icon icon-link"></span></a>查看 MySQL 信息</h3><div class="wrap-body">
<pre class="language-shell"><code class="language-shell code-highlight"><span class="code-line"><span class="token comment"># 显示当前mysql的version的各种信息</span>
</span><span class="code-line">mysql<span class="token operator">></span> status<span class="token punctuation">;</span>
</span><span class="code-line"><span class="token comment"># 显示当前mysql的version信息</span>
</span><span class="code-line">mysql<span class="token operator">></span> <span class="token keyword">select</span> version<span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</span><span class="code-line"><span class="token comment"># 查看 MySQL 端口号</span>
</span><span class="code-line">mysql<span class="token operator">></span> show global variables like <span class="token string">'port'</span><span class="token punctuation">;</span>
</span></code></pre>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="退出mysql会话"><a aria-hidden="true" tabindex="-1" href="#退出mysql会话"><span class="icon icon-link"></span></a>退出MySQL会话</h3><div class="wrap-body">
<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line">mysql<span class="token operator">></span> <span class="token builtin class-name">exit</span>
</span></code></pre>
<p>退出 <code>quit;</code> 或 <code>\q;</code> 一样的效果</p>
</div></div></div><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="备份"><a aria-hidden="true" tabindex="-1" href="#备份"><span class="icon icon-link"></span></a>备份</h3><div class="wrap-body">
<!--rehype:wrap-class=col-span-2-->
<p>备份特定表</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysqldump <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name table1 table2 <span class="token operator">></span> tables_backup.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>备份多个数据库</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysqldump <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> <span class="token parameter variable">--databases</span> db1 db2 <span class="token operator">></span> multi_backup.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>备份所有数据库</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysqldump <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> --all-databases <span class="token operator">></span> all_backup.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>备份时压缩</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysqldump <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name <span class="token operator">|</span> <span class="token function">gzip</span> <span class="token operator">></span> db_backup.sql.gz
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>导出不带架构的数据库</p>
<pre class="wrap-text "><code class="language-shell code-highlight"><span class="code-line">mysqldump <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name --no-data<span class="token operator">=</span>true --add-drop-table<span class="token operator">=</span>false <span class="token operator">></span> db.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>仅导出数据</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysqldump <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> --no-create-info db_name <span class="token operator">></span> only_data.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>仅导出结构</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysqldump <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> --no-data db_name <span class="token operator">></span> only_schema.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>导出时忽略某些表</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysqldump <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name --ignore-table<span class="token operator">=</span>db_name.table1 --ignore-table<span class="token operator">=</span>db_name.table2 <span class="token operator">></span> partial.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
</div></div></div><div class="wrap h3body-not-exist row-span-2"><div class="wrap-header h3wrap"><h3 id="恢复备份"><a aria-hidden="true" tabindex="-1" href="#恢复备份"><span class="icon icon-link"></span></a>恢复备份</h3><div class="wrap-body">
<!--rehype:wrap-class=row-span-2-->
<p>恢复单个数据库备份</p>
<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line">mysql <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name <span class="token operator">&#x3C;</span> db_backup.sql
</span></code></pre>
<p>恢复多个数据库（带 <code>--databases</code> 选项备份的）</p>
<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line">mysql <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> <span class="token operator">&#x3C;</span> multi_backup.sql
</span></code></pre>
<p>恢复所有数据库（使用 <code>--all-databases</code> 备份的）</p>
<pre class="language-bash"><code class="language-bash code-highlight"><span class="code-line">mysql <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> <span class="token operator">&#x3C;</span> all_backup.sql
</span></code></pre>
<p>从 gzip 压缩的备份恢复</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">gunzip <span class="token operator">&#x3C;</span> db_backup.sql.gz <span class="token operator">|</span> mysql <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name
</span><span class="code-line">
</span><span class="code-line"><span class="token comment"># 或：</span>
</span><span class="code-line">
</span><span class="code-line">zcat db_backup.sql.gz <span class="token operator">|</span> mysql <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>恢复单张表（从 <code>mysqldump</code> 单表导出文件）</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysql <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name <span class="token operator">&#x3C;</span> table1_backup.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>先创建数据库再导入（如果备份中不包含 CREATE DATABASE）</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysql <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> <span class="token parameter variable">-e</span> <span class="token string">"CREATE DATABASE IF NOT EXISTS db_name;"</span>
</span><span class="code-line">
</span><span class="code-line">mysql <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name <span class="token operator">&#x3C;</span> db_backup.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>恢复指定字符集（防止乱码）</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysql --default-character-set<span class="token operator">=</span>utf8mb4 <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name <span class="token operator">&#x3C;</span> db_backup.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>恢复时跳过某些错误（如重复键）</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysql <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> <span class="token parameter variable">--force</span> db_name <span class="token operator">&#x3C;</span> db_backup.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
<p>恢复到远程主机数据库</p>
<pre class="wrap-text "><code class="language-bash code-highlight"><span class="code-line">mysql <span class="token parameter variable">-h</span> remote_host <span class="token parameter variable">-u</span> user <span class="token parameter variable">-p</span> db_name <span class="token operator">&#x3C;</span> db_backup.sql
</span></code></pre>
<!--rehype:className=wrap-text -->
</div></div></div><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="错误处理error-handling"><a aria-hidden="true" tabindex="-1" href="#错误处理error-handling"><span class="icon icon-link"></span></a>错误处理（Error Handling）</h3><div class="wrap-body">
<!--rehype:wrap-class=col-span-2-->
<table class="left-align"><thead><tr><th align="left">语句</th><th align="left">说明</th></tr></thead><tbody><tr><td align="left"><code>SHOW ERRORS;</code></td><td align="left">显示最近的错误</td></tr><tr><td align="left"><code>SHOW WARNINGS;</code></td><td align="left">显示最近的警告</td></tr><tr><td align="left"><code>SHOW COUNT(*) ERRORS;</code></td><td align="left">显示错误数量</td></tr><tr><td align="left"><code>SHOW COUNT(*) WARNINGS;</code></td><td align="left">显示警告数量</td></tr><tr><td align="left"><code>EXPLAIN SELECT ...;</code></td><td align="left">分析查询执行计划</td></tr><tr><td align="left"><code>SHOW ENGINE INNODB STATUS;</code></td><td align="left">查看 InnoDB 状态和死锁信息</td></tr><tr><td align="left"><code>SHOW PROFILE;</code></td><td align="left">显示语句的资源消耗（需开启 profiling）</td></tr><tr><td align="left"><code>SHOW PROFILES;</code></td><td align="left">显示所有已记录的 profiling 数据</td></tr><tr><td align="left"><code>SHOW PROCESSLIST;</code></td><td align="left">查看当前线程，排查长时间运行或阻塞的语句</td></tr><tr><td align="left"><code>SHOW STATUS LIKE 'Last_error%';</code></td><td align="left">查看上次语句执行的错误信息</td></tr><tr><td align="left"><code>SHOW VARIABLES LIKE 'log_%';</code></td><td align="left">查看错误日志相关配置</td></tr><tr><td align="left"><code>SHOW BINARY LOGS;</code></td><td align="left">查看二进制日志，排查事务或复制异常</td></tr><tr><td align="left"><code>SHOW SLAVE STATUS\G</code></td><td align="left">查看主从复制错误（用于主从复制场景）</td></tr><tr><td align="left"><code>SHOW MASTER STATUS;</code></td><td align="left">查看主库状态，辅助分析复制问题</td></tr></tbody></table>
<!--rehype:className=left-align-->
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="mysql-示例"><a aria-hidden="true" tabindex="-1" href="#mysql-示例"><span class="icon icon-link"></span></a>MySQL 示例</h2><div class="wrap-body">
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="管理表格"><a aria-hidden="true" tabindex="-1" href="#管理表格"><span class="icon icon-link"></span></a>管理表格</h3><div class="wrap-body">
<p>创建一个包含三列的新表</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">(</span>
</span><span class="code-line"> id <span class="token keyword">INT</span><span class="token punctuation">,</span>
</span><span class="code-line"> name <span class="token keyword">VARCHAR</span> <span class="token keyword">DEFAULT</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span>
</span><span class="code-line"> price <span class="token keyword">INT</span> <span class="token keyword">DEFAULT</span> <span class="token number">0</span>
</span><span class="code-line"> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">(</span>id<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token punctuation">)</span><span class="token punctuation">;</span>
</span></code></pre>
<p>从数据库中删除表</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">DROP</span> <span class="token keyword">TABLE</span> t <span class="token punctuation">;</span>
</span></code></pre>
<p>向表中添加新列</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> t <span class="token keyword">ADD</span> <span class="token keyword">column</span><span class="token punctuation">;</span>
</span></code></pre>
<p>从表中删除列c</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> t <span class="token keyword">DROP</span> <span class="token keyword">COLUMN</span> c <span class="token punctuation">;</span>
</span></code></pre>
<p>添加约束</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> t <span class="token keyword">ADD</span> <span class="token keyword">constraint</span><span class="token punctuation">;</span>
</span></code></pre>
<p>删除约束</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> t <span class="token keyword">DROP</span> <span class="token keyword">constraint</span><span class="token punctuation">;</span>
</span></code></pre>
<p>将表从t1重命名为t2</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> t1 <span class="token keyword">RENAME</span> <span class="token keyword">TO</span> t2<span class="token punctuation">;</span>
</span></code></pre>
<p>将列 c1 重命名为 c2</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> t1 CHANGE c1 c2 datatype<span class="token punctuation">;</span>
</span><span class="code-line"><span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> table_name <span class="token keyword">RENAME</span> <span class="token keyword">COLUMN</span> c1 <span class="token keyword">TO</span> c2<span class="token punctuation">;</span>
</span></code></pre>
<p>将列c1的数据类型改为datatype</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">ALTER</span> <span class="token keyword">TABLE</span> t1 <span class="token keyword">MODIFY</span> c1 datatype<span class="token punctuation">;</span>
</span></code></pre>
<p>删除表中的所有数据</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">TRUNCATE</span> <span class="token keyword">TABLE</span> t<span class="token punctuation">;</span>
</span></code></pre>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="从表中查询数据"><a aria-hidden="true" tabindex="-1" href="#从表中查询数据"><span class="icon icon-link"></span></a>从表中查询数据</h3><div class="wrap-body">
<p>从表中查询列c1、c2中的数据</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t
</span></code></pre>
<p>查询表中的所有行和列</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> <span class="token operator">*</span> <span class="token keyword">FROM</span> t
</span></code></pre>
<p>查询数据并使用条件筛选行</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">WHERE</span> condition
</span></code></pre>
<p>查询表中的不同行</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> <span class="token keyword">DISTINCT</span> c1 <span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">WHERE</span> condition
</span></code></pre>
<p>按升序或降序对结果集排序</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">ORDER</span> <span class="token keyword">BY</span> c1 <span class="token keyword">ASC</span> <span class="token punctuation">[</span><span class="token keyword">DESC</span><span class="token punctuation">]</span>
</span></code></pre>
<p>跳过行的偏移并返回下n行</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">ORDER</span> <span class="token keyword">BY</span> c1
</span><span class="code-line"><span class="token keyword">LIMIT</span> n <span class="token keyword">OFFSET</span> <span class="token keyword">offset</span>
</span></code></pre>
<p>使用聚合函数对行进行分组</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> aggregate<span class="token punctuation">(</span>c2<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">GROUP</span> <span class="token keyword">BY</span> c1
</span></code></pre>
<p>使用HAVING子句筛选组</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> aggregate<span class="token punctuation">(</span>c2<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">GROUP</span> <span class="token keyword">BY</span> c1
</span><span class="code-line"><span class="token keyword">HAVING</span> condition
</span></code></pre>
</div></div></div><div class="wrap h3body-not-exist row-span-2"><div class="wrap-header h3wrap"><h3 id="从多个表查询"><a aria-hidden="true" tabindex="-1" href="#从多个表查询"><span class="icon icon-link"></span></a>从多个表查询</h3><div class="wrap-body">
<!--rehype:wrap-class=row-span-2-->
<p>内部连接 t1 和 t2</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t1
</span><span class="code-line"><span class="token keyword">INNER</span> <span class="token keyword">JOIN</span> t2 <span class="token keyword">ON</span> condition
</span></code></pre>
<p>左连接t1和t1</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t1
</span><span class="code-line"><span class="token keyword">LEFT</span> <span class="token keyword">JOIN</span> t2 <span class="token keyword">ON</span> condition
</span></code></pre>
<p>右连接t1和t2</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t1
</span><span class="code-line"><span class="token keyword">RIGHT</span> <span class="token keyword">JOIN</span> t2 <span class="token keyword">ON</span> condition
</span></code></pre>
<p>执行完全外部连接</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t1
</span><span class="code-line"><span class="token keyword">FULL</span> <span class="token keyword">OUTER</span> <span class="token keyword">JOIN</span> t2 <span class="token keyword">ON</span> condition
</span></code></pre>
<p>生成表中行的笛卡尔积</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t1
</span><span class="code-line"><span class="token keyword">CROSS</span> <span class="token keyword">JOIN</span> t2
</span></code></pre>
<p>执行交叉连接的另一种方法</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t1<span class="token punctuation">,</span> t2
</span></code></pre>
<p>使用INNER Join子句将t1连接到自身</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t1 A
</span><span class="code-line"><span class="token keyword">INNER</span> <span class="token keyword">JOIN</span> t1 B <span class="token keyword">ON</span> condition
</span></code></pre>
<p>使用SQL运算符，合并两个查询中的行</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t1
</span><span class="code-line"><span class="token keyword">UNION</span> <span class="token punctuation">[</span><span class="token keyword">ALL</span><span class="token punctuation">]</span>
</span><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t2
</span></code></pre>
<p>返回两个查询的交集</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t1
</span><span class="code-line"><span class="token keyword">INTERSECT</span>
</span><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t2
</span></code></pre>
<p>从另一个结果集中减去一个结果集</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t1
</span><span class="code-line">MINUS
</span><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t2
</span></code></pre>
<p>使用模式匹配%查询行_</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t1
</span><span class="code-line"><span class="token keyword">WHERE</span> c1 <span class="token punctuation">[</span><span class="token operator">NOT</span><span class="token punctuation">]</span> <span class="token operator">LIKE</span> pattern
</span></code></pre>
<p>查询列表中的行</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">WHERE</span> c1 <span class="token punctuation">[</span><span class="token operator">NOT</span><span class="token punctuation">]</span> <span class="token operator">IN</span> value_list
</span></code></pre>
<p>查询两个值之间的行</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">WHERE</span> c1 <span class="token operator">BETWEEN</span> low <span class="token operator">AND</span> high
</span></code></pre>
<p>检查表中的值是否为NULL</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2 <span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">WHERE</span> c1 <span class="token operator">IS</span> <span class="token punctuation">[</span><span class="token operator">NOT</span><span class="token punctuation">]</span> <span class="token boolean">NULL</span>
</span></code></pre>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="使用-sql-约束"><a aria-hidden="true" tabindex="-1" href="#使用-sql-约束"><span class="icon icon-link"></span></a>使用 SQL 约束</h3><div class="wrap-body">
<p>将c1和c2设置为主键</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t<span class="token punctuation">(</span>
</span><span class="code-line"> c1 <span class="token keyword">INT</span><span class="token punctuation">,</span> c2 <span class="token keyword">INT</span><span class="token punctuation">,</span> c3 <span class="token keyword">VARCHAR</span><span class="token punctuation">,</span>
</span><span class="code-line"> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span> <span class="token punctuation">(</span>c1<span class="token punctuation">,</span>c2<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token punctuation">)</span><span class="token punctuation">;</span>
</span></code></pre>
<p>将c2列设置为外键</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t1<span class="token punctuation">(</span>
</span><span class="code-line"> c1 <span class="token keyword">INT</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">,</span>
</span><span class="code-line"> c2 <span class="token keyword">INT</span><span class="token punctuation">,</span>
</span><span class="code-line"> <span class="token keyword">FOREIGN</span> <span class="token keyword">KEY</span> <span class="token punctuation">(</span>c2<span class="token punctuation">)</span> <span class="token keyword">REFERENCES</span> t2<span class="token punctuation">(</span>c2<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token punctuation">)</span><span class="token punctuation">;</span>
</span></code></pre>
<p>使c1和c2中的值唯一</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t<span class="token punctuation">(</span>
</span><span class="code-line"> c1 <span class="token keyword">INT</span><span class="token punctuation">,</span> c1 <span class="token keyword">INT</span><span class="token punctuation">,</span>
</span><span class="code-line"> <span class="token keyword">UNIQUE</span><span class="token punctuation">(</span>c2<span class="token punctuation">,</span>c3<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token punctuation">)</span><span class="token punctuation">;</span>
</span></code></pre>
<p>确保c1>0和c1>=c2中的值</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t<span class="token punctuation">(</span>
</span><span class="code-line"> c1 <span class="token keyword">INT</span><span class="token punctuation">,</span> c2 <span class="token keyword">INT</span><span class="token punctuation">,</span>
</span><span class="code-line"> <span class="token keyword">CHECK</span><span class="token punctuation">(</span>c1<span class="token operator">></span> <span class="token number">0</span> <span class="token operator">AND</span> c1 <span class="token operator">>=</span> c2<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token punctuation">)</span><span class="token punctuation">;</span>
</span></code></pre>
<p>c2列中的设置值不为NULL</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">TABLE</span> t<span class="token punctuation">(</span>
</span><span class="code-line"> c1 <span class="token keyword">INT</span> <span class="token keyword">PRIMARY</span> <span class="token keyword">KEY</span><span class="token punctuation">,</span>
</span><span class="code-line"> c2 <span class="token keyword">VARCHAR</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span>
</span><span class="code-line"><span class="token punctuation">)</span><span class="token punctuation">;</span>
</span></code></pre>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="修改数据"><a aria-hidden="true" tabindex="-1" href="#修改数据"><span class="icon icon-link"></span></a>修改数据</h3><div class="wrap-body">
<p>在表格中插入一行</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t<span class="token punctuation">(</span>column_list<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token keyword">VALUES</span><span class="token punctuation">(</span>value_list<span class="token punctuation">)</span><span class="token punctuation">;</span>
</span></code></pre>
<p>在表格中插入多行</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t<span class="token punctuation">(</span>column_list<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token keyword">VALUES</span> <span class="token punctuation">(</span>value_list<span class="token punctuation">)</span><span class="token punctuation">,</span>
</span><span class="code-line"> <span class="token punctuation">(</span>value_list<span class="token punctuation">)</span><span class="token punctuation">,</span> …<span class="token punctuation">;</span>
</span></code></pre>
<p>将行从t2插入t1</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">INSERT</span> <span class="token keyword">INTO</span> t1<span class="token punctuation">(</span>column_list<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token keyword">SELECT</span> column_list
</span><span class="code-line"><span class="token keyword">FROM</span> t2<span class="token punctuation">;</span>
</span></code></pre>
<p>更新列c1中所有行的新值</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">UPDATE</span> t
</span><span class="code-line"><span class="token keyword">SET</span> c1 <span class="token operator">=</span> new_value<span class="token punctuation">;</span>
</span></code></pre>
<p>更新列c1、c2中与条件匹配的值</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">UPDATE</span> t
</span><span class="code-line"><span class="token keyword">SET</span> c1 <span class="token operator">=</span> new_value<span class="token punctuation">,</span>
</span><span class="code-line"> c2 <span class="token operator">=</span> new_value
</span><span class="code-line"><span class="token keyword">WHERE</span> condition<span class="token punctuation">;</span>
</span></code></pre>
<p>删除表中的所有数据</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">DELETE</span> <span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
</span></code></pre>
<p>删除表中的行子集</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">DELETE</span> <span class="token keyword">FROM</span> t
</span><span class="code-line"><span class="token keyword">WHERE</span> condition<span class="token punctuation">;</span>
</span></code></pre>
</div></div></div><div class="wrap h3body-not-exist row-span-2"><div class="wrap-header h3wrap"><h3 id="管理视图"><a aria-hidden="true" tabindex="-1" href="#管理视图"><span class="icon icon-link"></span></a>管理视图</h3><div class="wrap-body">
<!--rehype:wrap-class=row-span-2-->
<p>创建由c1和c2组成的新视图</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">VIEW</span> v<span class="token punctuation">(</span>c1<span class="token punctuation">,</span>c2<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token keyword">AS</span>
</span><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
</span></code></pre>
<p>使用选中选项创建新视图</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">VIEW</span> v<span class="token punctuation">(</span>c1<span class="token punctuation">,</span>c2<span class="token punctuation">)</span>
</span><span class="code-line"><span class="token keyword">AS</span>
</span><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
</span><span class="code-line"><span class="token keyword">WITH</span> <span class="token punctuation">[</span><span class="token keyword">CASCADED</span> <span class="token operator">|</span> <span class="token keyword">LOCAL</span><span class="token punctuation">]</span> <span class="token keyword">CHECK</span> <span class="token keyword">OPTION</span><span class="token punctuation">;</span>
</span></code></pre>
<p>创建递归视图</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> RECURSIVE <span class="token keyword">VIEW</span> v
</span><span class="code-line"><span class="token keyword">AS</span>
</span><span class="code-line"><span class="token keyword">select</span><span class="token operator">-</span>statement <span class="token comment">-- anchor part</span>
</span><span class="code-line"><span class="token keyword">UNION</span> <span class="token punctuation">[</span><span class="token keyword">ALL</span><span class="token punctuation">]</span>
</span><span class="code-line"><span class="token keyword">select</span><span class="token operator">-</span>statement<span class="token punctuation">;</span> <span class="token comment">-- recursive part</span>
</span></code></pre>
<p>创建临时视图</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">TEMPORARY</span> <span class="token keyword">VIEW</span> v
</span><span class="code-line"><span class="token keyword">AS</span>
</span><span class="code-line"><span class="token keyword">SELECT</span> c1<span class="token punctuation">,</span> c2
</span><span class="code-line"><span class="token keyword">FROM</span> t<span class="token punctuation">;</span>
</span></code></pre>
<p>删除视图</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">DROP</span> <span class="token keyword">VIEW</span> view_name<span class="token punctuation">;</span>
</span></code></pre>
</div></div></div><div class="wrap h3body-exist"><div class="wrap-header h3wrap"><h3 id="管理触发器"><a aria-hidden="true" tabindex="-1" href="#管理触发器"><span class="icon icon-link"></span></a>管理触发器</h3><div class="wrap-body">
<p>创建或修改触发器</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token operator">OR</span> <span class="token keyword">MODIFY</span> <span class="token keyword">TRIGGER</span> trigger_name
</span><span class="code-line"><span class="token keyword">WHEN</span> EVENT
</span><span class="code-line"><span class="token keyword">ON</span> table_name TRIGGER_TYPE
</span><span class="code-line"><span class="token keyword">EXECUTE</span> stored_procedure<span class="token punctuation">;</span>
</span></code></pre>
<h4 id="when"><a aria-hidden="true" tabindex="-1" href="#when"><span class="icon icon-link"></span></a>WHEN</h4>
<table><thead><tr><th align="left">:-</th><th align="left">:-</th></tr></thead><tbody><tr><td align="left"><code>BEFORE</code></td><td align="left">在事件发生前调用</td></tr><tr><td align="left"><code>AFTER</code></td><td align="left">事件发生后调用</td></tr></tbody></table>
<h4 id="event"><a aria-hidden="true" tabindex="-1" href="#event"><span class="icon icon-link"></span></a>EVENT</h4>
<table><thead><tr><th align="left">:-</th><th align="left">:-</th></tr></thead><tbody><tr><td align="left"><code>INSERT</code></td><td align="left">为INSERT调用</td></tr><tr><td align="left"><code>UPDATE</code></td><td align="left">调用UPDATE</td></tr><tr><td align="left"><code>DELETE</code></td><td align="left">调用DELETE</td></tr></tbody></table>
<h4 id="trigger_type"><a aria-hidden="true" tabindex="-1" href="#trigger_type"><span class="icon icon-link"></span></a>TRIGGER_TYPE</h4>
<table><thead><tr><th align="left">:-</th><th align="left">:-</th></tr></thead><tbody><tr><td align="left"><code>FOR EACH ROW</code></td><td align="left">-</td></tr><tr><td align="left"><code>FOR EACH STATEMENT</code></td><td align="left">-</td></tr></tbody></table>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="管理索引"><a aria-hidden="true" tabindex="-1" href="#管理索引"><span class="icon icon-link"></span></a>管理索引</h3><div class="wrap-body">
<p>在t表的c1和c2上创建索引</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">INDEX</span> idx_name
</span><span class="code-line"><span class="token keyword">ON</span> t<span class="token punctuation">(</span>c1<span class="token punctuation">,</span>c2<span class="token punctuation">)</span><span class="token punctuation">;</span>
</span></code></pre>
<p>在t表的c3、c4上创建唯一索引</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">CREATE</span> <span class="token keyword">UNIQUE</span> <span class="token keyword">INDEX</span> idx_name
</span><span class="code-line"><span class="token keyword">ON</span> t<span class="token punctuation">(</span>c3<span class="token punctuation">,</span>c4<span class="token punctuation">)</span>
</span></code></pre>
<p>删除索引</p>
<pre class="language-sql"><code class="language-sql code-highlight"><span class="code-line"><span class="token keyword">DROP</span> <span class="token keyword">INDEX</span> idx_name <span class="token keyword">ON</span> t<span class="token punctuation">;</span>
</span></code></pre>
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="mysql-数据类型"><a aria-hidden="true" tabindex="-1" href="#mysql-数据类型"><span class="icon icon-link"></span></a>MySQL 数据类型</h2><div class="wrap-body">
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="strings"><a aria-hidden="true" tabindex="-1" href="#strings"><span class="icon icon-link"></span></a>Strings</h3><div class="wrap-body">
<table><thead><tr><th>-</th><th>-</th></tr></thead><tbody><tr><td><code>CHAR</code></td><td>String (0 - 255)</td></tr><tr><td><code>VARCHAR</code></td><td>String (0 - 255)</td></tr><tr><td><code>TINYTEXT</code></td><td>String (0 - 255)</td></tr><tr><td><code>TEXT</code></td><td>String (0 - 65535)</td></tr><tr><td><code>BLOB</code></td><td>String (0 - 65535)</td></tr><tr><td><code>MEDIUMTEXT</code></td><td>String (0 - 16777215)</td></tr><tr><td><code>MEDIUMBLOB</code></td><td>String (0 - 16777215)</td></tr><tr><td><code>LONGTEXT</code></td><td>String (0 - 429496­7295)</td></tr><tr><td><code>LONGBLOB</code></td><td>String (0 - 429496­7295)</td></tr><tr><td><code>ENUM</code></td><td>One of preset options</td></tr><tr><td><code>SET</code></td><td>Selection of preset options</td></tr></tbody></table>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="date--time"><a aria-hidden="true" tabindex="-1" href="#date--time"><span class="icon icon-link"></span></a>Date &#x26; time</h3><div class="wrap-body">
<table><thead><tr><th>Data Type</th><th>Format</th></tr></thead><tbody><tr><td><code>DATE</code></td><td>yyyy-MM-dd</td></tr><tr><td><code>TIME</code></td><td>hh:mm:ss</td></tr><tr><td><code>DATETIME</code></td><td>yyyy-MM-dd hh:mm:ss</td></tr><tr><td><code>TIMESTAMP</code></td><td>yyyy-MM-dd hh:mm:ss</td></tr><tr><td><code>YEAR</code></td><td>yyyy</td></tr></tbody></table>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="numeric"><a aria-hidden="true" tabindex="-1" href="#numeric"><span class="icon icon-link"></span></a>Numeric</h3><div class="wrap-body">
<table><thead><tr><th>-</th><th>-</th></tr></thead><tbody><tr><td><code>TINYINT x</code></td><td>Integer (-128 to 127)</td></tr><tr><td><code>SMALLINT x</code></td><td>Integer (-32768 to 32767)</td></tr><tr><td><code>MEDIUMINT x</code></td><td>Integer (-8388608 to 8388607)</td></tr><tr><td><code>INT x</code></td><td>Integer (-2147­483648 to 214748­3647)</td></tr><tr><td><code>BIGINT x</code></td><td>Integer (-9223­372­036­854­775808 to 922337­203­685­477­5807)</td></tr><tr><td><code>FLOAT</code></td><td>Decimal (precise to 23 digits)</td></tr><tr><td><code>DOUBLE</code></td><td>Decimal (24 to 53 digits)</td></tr><tr><td><code>DECIMAL</code></td><td>"­DOU­BLE­" stored as string</td></tr></tbody></table>
</div></div></div></div></div><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="函数"><a aria-hidden="true" tabindex="-1" href="#函数"><span class="icon icon-link"></span></a>函数</h2><div class="wrap-body">
</div></div><div class="h2wrap-body"><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="聚合函数"><a aria-hidden="true" tabindex="-1" href="#聚合函数"><span class="icon icon-link"></span></a>聚合函数</h3><div class="wrap-body">
<table><thead><tr><th align="left">函数</th><th align="left">解释</th></tr></thead><tbody><tr><td align="left"><code>SUM()</code></td><td align="left">计算一列值的总和</td></tr><tr><td align="left"><code>AVG()</code></td><td align="left">计算一列值的平均值</td></tr><tr><td align="left"><code>COUNT()</code></td><td align="left">计算行数，可选择性地忽略NULL值</td></tr><tr><td align="left"><code>MAX()</code></td><td align="left">找出一列的最大值</td></tr><tr><td align="left"><code>MIN()</code></td><td align="left">找出一列的最小值</td></tr><tr><td align="left"><code>GROUP_CONCAT()</code></td><td align="left">将一组值连接成单一字符串，可指定分隔符，常用于分组。</td></tr></tbody></table>
</div></div></div><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="数学函数"><a aria-hidden="true" tabindex="-1" href="#数学函数"><span class="icon icon-link"></span></a>数学函数</h3><div class="wrap-body">
<!--rehype:wrap-class=col-span-2 -->
<table><thead><tr><th align="left">函数</th><th align="left">解释</th><th align="left">示例语法</th><th align="left">结果</th></tr></thead><tbody><tr><td align="left"><code>ABS(x)</code></td><td align="left">返回数值的绝对值</td><td align="left"><code>ABS(-5)</code></td><td align="left">5</td></tr><tr><td align="left"><code>ROUND(x,y)</code></td><td align="left">四舍五入到指定的小数位数，y为小数位数，默认为0</td><td align="left"><code>ROUND(3.1415,2)</code></td><td align="left">3.14</td></tr><tr><td align="left"><code>FLOOR(x)</code></td><td align="left">向下取整至最接近的整数</td><td align="left"><code>FLOOR(3.7)</code></td><td align="left">3</td></tr><tr><td align="left"><code>CEIL(x)</code></td><td align="left">向上取整至最接近的整数</td><td align="left"><code>CEIL(3.3)</code></td><td align="left">4</td></tr><tr><td align="left"><code>SQRT(x)</code></td><td align="left">返回一个数的平方根</td><td align="left"><code>SQRT(16)</code></td><td align="left">4</td></tr><tr><td align="left"><code>MOD(x,y)</code></td><td align="left">返回x除以y的余数</td><td align="left"><code>MOD(10,3)</code></td><td align="left">1</td></tr><tr><td align="left"><code>RAND([seed])</code></td><td align="left">返回0到1之间的随机数，可选种子值</td><td align="left"><code>RAND()</code> 或 <code>RAND(123)</code></td><td align="left">0.345...</td></tr></tbody></table>
</div></div></div><div class="wrap h3body-not-exist"><div class="wrap-header h3wrap"><h3 id="日期和时间函数"><a aria-hidden="true" tabindex="-1" href="#日期和时间函数"><span class="icon icon-link"></span></a>日期和时间函数</h3><div class="wrap-body">
<table><thead><tr><th align="left">函数</th><th align="left">解释</th></tr></thead><tbody><tr><td align="left"><code>NOW()</code></td><td align="left">返回当前日期和时间</td></tr><tr><td align="left"><code>CURDATE()</code></td><td align="left">返回当前日期</td></tr><tr><td align="left"><code>CURTIME()</code></td><td align="left">返回当前时间</td></tr><tr><td align="left"><code>DATE_FORMAT()</code></td><td align="left">格式化日期时间输出</td></tr><tr><td align="left"><code>DATEDIFF()</code></td><td align="left">计算两个日期之间相差的天数</td></tr><tr><td align="left"><code>STR_TO_DATE()</code></td><td align="left">将字符串转换为日期格式</td></tr></tbody></table>
</div></div></div><div class="wrap h3body-not-exist col-span-2"><div class="wrap-header h3wrap"><h3 id="字符串函数"><a aria-hidden="true" tabindex="-1" href="#字符串函数"><span class="icon icon-link"></span></a>字符串函数</h3><div class="wrap-body">
<!--rehype:wrap-class=col-span-2 -->
<table><thead><tr><th align="left">函数</th><th align="left">解释</th><th>示例语法</th><th>结果</th></tr></thead><tbody><tr><td align="left"><code>CONCAT(s1,s2,...)</code></td><td align="left">连接两个或更多字符串</td><td><code>CONCAT('Hello, ','World!')</code></td><td>'Hello, World!'</td></tr><tr><td align="left"><code>LOWER(str)</code></td><td align="left">转换为小写</td><td><code>LOWER('HELLO')</code></td><td>'hello'</td></tr><tr><td align="left"><code>UPPER(str)</code></td><td align="left">转换为大写</td><td><code>UPPER('world')</code></td><td>'WORLD'</td></tr><tr><td align="left"><code>TRIM(str)</code></td><td align="left">去除字符串两端空格</td><td><code>TRIM(' Hello ')</code></td><td>'Hello'</td></tr><tr><td align="left"><code>LEFT(str,len)</code></td><td align="left">提取字符串左侧的若干字符</td><td><code>LEFT('Hello', 3)</code></td><td>'Hel'</td></tr><tr><td align="left"><code>RIGHT(str,len)</code></td><td align="left">提取字符串右侧的若干字符</td><td><code>RIGHT('Hello', 2)</code></td><td>'lo'</td></tr><tr><td align="left"><code>SUBSTR(str,pos,len)</code></td><td align="left">提取字符串中的一部分</td><td><code>SUBSTR('Hello', 2, 3)</code></td><td>'ell'</td></tr><tr><td align="left"><code>REPLACE(str,from_str,to_str)</code></td><td align="left">替换字符串中的部分文本</td><td><code>REPLACE('Hello', 'l', 'L')</code></td><td>'HeLLo'</td></tr></tbody></table>
</div></div></div><div class="wrap h3body-not-exist col-span-3"><div class="wrap-header h3wrap"><h3 id="高级函数"><a aria-hidden="true" tabindex="-1" href="#高级函数"><span class="icon icon-link"></span></a>高级函数</h3><div class="wrap-body">
<!--rehype:wrap-class=col-span-3 -->
<table><thead><tr><th>函数</th><th>解释</th><th>示例语法</th><th>结果</th></tr></thead><tbody><tr><td>BIN(x)</td><td>返回 x 的二进制编码，x 为十进制数。</td><td><code>BIN(2)</code></td><td><code>10</code></td></tr><tr><td>BINARY(s)</td><td>将字符串 s 转换为二进制字符串。</td><td><code>BINARY 'RUNOOB'</code></td><td><code>'RUNOOB'</code>（显示效果，实际存储为二进制）</td></tr><tr><td>CASE</td><td>复合条件函数，根据条件返回不同结果。</td><td><code>CASE WHEN 1 > 0 THEN '1 > 0' WHEN 2 > 0 THEN '2 > 0' ELSE '3 > 0' END</code></td><td><code>'1 > 0'</code></td></tr><tr><td>CAST(x AS type)</td><td>转换数据类型。</td><td><code>CAST('2017-08-29' AS DATE)</code></td><td><code>2017-08-29</code></td></tr><tr><td>COALESCE(expr1, expr2, ..., expr_n)</td><td>返回第一个非空表达式的值。</td><td><code>COALESCE(NULL, NULL, 'runoob.com', NULL, 'google.com')</code></td><td><code>'runoob.com'</code></td></tr><tr><td>CONNECTION_ID()</td><td>返回当前连接的唯一ID。</td><td><code>CONNECTION_ID()</code></td><td><code>4292835</code>（示例值）</td></tr><tr><td>CONV(x, f1, f2)</td><td>将 f1 进制数转换为 f2 进制数。</td><td><code>CONV(15, 10, 2)</code></td><td><code>1111</code></td></tr><tr><td>CONVERT(s USING cs)</td><td>转换字符串 s 的字符集为 cs。</td><td><code>CHARSET(CONVERT('ABC' USING gbk))</code></td><td><code>gbk</code></td></tr><tr><td>CURRENT_USER()</td><td>返回当前用户。</td><td><code>CURRENT_USER()</code></td><td><code>guest@%</code></td></tr><tr><td>DATABASE()</td><td>返回当前数据库名。</td><td><code>DATABASE()</code></td><td><code>runoob</code></td></tr><tr><td>IF(expr, v1, v2)</td><td>条件表达式，expr 为真则 v1，否则 v2。</td><td><code>IF(1 > 0, '正确', '错误')</code></td><td><code>'正确'</code></td></tr><tr><td>IFNULL(v1, v2)</td><td>如果 v1 不为 NULL，则返回 v1，否则返回 v2。</td><td><code>IFNULL(NULL, 'Hello Word')</code></td><td><code>'Hello Word'</code></td></tr><tr><td>ISNULL(expression)</td><td>判断表达式是否为 NULL。</td><td><code>ISNULL(NULL)</code></td><td><code>1</code></td></tr><tr><td>LAST_INSERT_ID()</td><td>返回最近生成的 AUTO_INCREMENT 值。</td><td><code>LAST_INSERT_ID()</code></td><td><code>6</code>（示例值）</td></tr><tr><td>NULLIF(expr1, expr2)</td><td>若 expr1 等于 expr2，则返回 NULL，否则返回 expr1。</td><td><code>NULLIF(25, 25)</code></td><td><code>NULL</code></td></tr></tbody></table>
</div></div></div></div></div><div class="wrap h2body-not-exist"><div class="wrap-header h2wrap"><h2 id="另见"><a aria-hidden="true" tabindex="-1" href="#另见"><span class="icon icon-link"></span></a>另见</h2><div class="wrap-body">
<ul>
<li><a href="http://www.w3school.com.cn/sql/index.asp">SQL 基础教程</a> <em>(w3school.com.cn)</em></li>
<li><a href="http://www.1keydata.com/cn/sql/sql-count.php">SQL 语句教程</a> <em>(1keydata.com)</em></li>
<li><a href="https://jaywcjlove.github.io/mysql-tutorial/21-minutes-MySQL-basic-entry.html">21分钟 MySQL 基础入门</a> <em>(jaywcjlove.github.io)</em></li>
</ul>
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