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has-sidebar" id="VPContent" data-v-736e9fd5 data-v-c231cb07><div class="VPDoc has-sidebar has-aside" data-v-c231cb07 data-v-01a78eb7><!--[--><!--]--><div class="container" data-v-01a78eb7><div class="aside" data-v-01a78eb7><div class="aside-curtain" data-v-01a78eb7></div><div class="aside-container" data-v-01a78eb7><div class="aside-content" data-v-01a78eb7><div class="VPDocAside" data-v-01a78eb7 data-v-e932614f><!--[--><!--]--><!--[--><!--]--><nav aria-labelledby="doc-outline-aria-label" class="VPDocAsideOutline" data-v-e932614f data-v-2f894604><div class="content" data-v-2f894604><div class="outline-marker" data-v-2f894604></div><div aria-level="2" class="outline-title" id="doc-outline-aria-label" role="heading" data-v-2f894604>On this page</div><ul class="VPDocOutlineItem root" data-v-2f894604 data-v-f41cfbc6><!--[--><!--]--></ul></div></nav><!--[--><!--]--><div class="spacer" data-v-e932614f></div><!--[--><!--]--><!----><!--[--><!--]--><!--[--><!--]--></div></div></div></div><div class="content" data-v-01a78eb7><div class="content-container" data-v-01a78eb7><!--[--><!--]--><main class="main" data-v-01a78eb7><div style="position:relative;" class="vp-doc _note_MySQL" data-v-01a78eb7><div><h1 id="mysql" tabindex="-1">MySQL <a class="header-anchor" href="#mysql" aria-label="Permalink to "MySQL""></a></h1><h2 id="mysql基础篇" tabindex="-1">MySQL基础篇 <a class="header-anchor" href="#mysql基础篇" aria-label="Permalink to "MySQL基础篇""></a></h2><h3 id="mysql简单使用" tabindex="-1">MySQL简单使用 <a class="header-anchor" href="#mysql简单使用" aria-label="Permalink to "MySQL简单使用""></a></h3><p>在命令行窗口输入</p><div class="language-sh vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">mysql</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> -uroot</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> -p1234</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> -hlocalhost</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> -P3306</span></span></code></pre></div><p>指定用户名为 <code>root</code> 密码为 <code>1234</code> 连接host为 <code>localhost</code> 端口号为 <code>3306</code></p><p>除了以明文方式输入密码，也可以通过另一种方式登录：</p><div class="language-sh vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">mysql</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> -u</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> root</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> -p</span></span>
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<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">1234</span></span></code></pre></div><p>进入mysql命令行工具后，查看所有表：</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">show databases;</span></span></code></pre></div><p>MySQL默认为我们创建了四个表<code> information_schema</code> <code>mysql</code> <code>performance_schema</code> <code>sys</code></p><p>创建一个新的数据库：</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">create</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> database</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> dbtest1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span></code></pre></div><p>使用数据库：</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">use</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> dbtest1;</span></span></code></pre></div><p>创建一张表，初始化<code>id</code>与<code>name</code>字段：</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">create</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> employees</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(id </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">int</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">name</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> varchar</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">15</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">));</span></span></code></pre></div><p>查看表中数据：</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">select</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> *</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> emoloyees;</span></span></code></pre></div><p>插入一条数据：</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">insert into</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> employees </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">values</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1001</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'Tom'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">insert into</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> employees </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">values</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1002</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'Jack'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span></code></pre></div><p>当我们向表中插入中文数据时，<code>5.7</code>版本的MySQL会报错，而<code>8.0</code>版本则不会：</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">insert into</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> employees </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">values</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1003</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'杰瑞'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span></code></pre></div><p>检查一下表的信息：</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">show </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">create</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> employees;</span></span></code></pre></div><p>可以发现，表的默认字符集是 <code>CHARSET=latin1</code> 拉丁字符集，不包含汉字。</p><p>查看编码与比较规则：</p><p>百分号<code>%</code>表示一个到多个字符</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">show variables </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">like</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> 'character_%'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">show variables </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">like</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> 'collation_%'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span></code></pre></div><p>若是<code>5.7</code>版本，默认的编码字符集为<code>latin1</code>，而最新的<code>8.0</code>为<code>utf8</code>。配置文件可以在<code>my.ini</code>中修改</p><p>删除一个数据库</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">drop</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> database</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> dbtest1;</span></span></code></pre></div><h3 id="基本的select语句" tabindex="-1">基本的SELECT语句 <a class="header-anchor" href="#基本的select语句" aria-label="Permalink to "基本的SELECT语句""></a></h3><h4 id="sql分类" tabindex="-1">SQL分类 <a class="header-anchor" href="#sql分类" aria-label="Permalink to "SQL分类""></a></h4><ul><li>DDL <code>DataDefinitionLanguage</code> 用于定义数据库对象（数据库 表 字段） <ul><li>主要语句关键字包括<code>CREATE</code> <code>DROP</code> <code>ALERT</code>等</li></ul></li><li>DML <code>DataManipulationLanguage</code> 用于对数据库表中的数据进行增删改查 <ul><li>主要语句关键字包括<code>INSERT</code> <code>DELETE</code> <code>UPDATE</code> <code>SELECT</code>等</li><li><code>SELECT</code>是SQL语言的基础，最为重要</li></ul></li><li>DQL <code>DataQueryLanguage</code> 用来查询数据库中表的记录 <ul><li>由于查询语句使用的非常频繁，将查询语句单拎出来自成一类</li></ul></li><li>DCL <code>DataControlLanguage</code> 用来创建数据库用户、控制数据库的访问权限 <ul><li>主要的语句关键字包括<code>GRANT</code> <code>REVOKE</code> <code>COMMIT</code> <code>ROLLBACK</code> <code>SAVEPOINT</code>等</li></ul></li></ul><h3 id="sql规则和规范" tabindex="-1">SQL规则和规范 <a class="header-anchor" href="#sql规则和规范" aria-label="Permalink to "SQL规则和规范""></a></h3><ul><li>SQL语句可以单行或多行书写，为了提高可读性，各子句分行写，必要时使用缩进，<strong>以分号结尾</strong></li><li>每条命令以 <code>;</code> 或 <code>\g</code> 或 <code>\G</code> 结束</li><li>关键字不能被缩写也不能分行</li><li>关于标点符号 <ul><li>必须保证所有的()、单引号、双引号是成对结束的</li><li>必须使用英文状态下的半角输入方式</li><li>字符串型和日期时间类型的数据可以使用单引号（' '）表示</li><li>列的别名，尽量使用双引号（" "），而且不建议省略as</li></ul></li></ul><h4 id="sql大小写规则" tabindex="-1">SQL大小写规则 <a class="header-anchor" href="#sql大小写规则" aria-label="Permalink to "SQL大小写规则""></a></h4><ul><li>MySQL 在 Windows 环境下是大小写不敏感的</li><li>MySQL 在 Linux 环境下是大小写敏感的 <ul><li>数据库名、表名、表的别名、变量名是严格区分大小写的</li><li>关键字、函数名、列名(或字段名)、列的别名(字段的别名) 是忽略大小写的。</li></ul></li><li>推荐采用统一的书写规范： <ul><li>数据库名、表名、表别名、字段名、字段别名等都小写</li><li>SQL 关键字、函数名、绑定变量等都大写</li></ul></li></ul><h4 id="注释书写方法" tabindex="-1">注释书写方法 <a class="header-anchor" href="#注释书写方法" aria-label="Permalink to "注释书写方法""></a></h4><ul><li>单行注释：<code>--注释内容</code> 或 <code># 注释内容</code> （MySQL独有）</li><li>多行注释: /* 注释内容 */</li></ul><h4 id="ddl-数据库操作" tabindex="-1">DDL - 数据库操作 <a class="header-anchor" href="#ddl-数据库操作" aria-label="Permalink to "DDL - 数据库操作""></a></h4><ul><li>查询 <ul><li>查询所有数据库 <code>SHOW DATABASES;</code></li><li>查询当前数据库 <code>SELECT DATABASE();</code></li></ul></li><li>创建 <ul><li><code>CREATE DATABASE [IF NOT EXISTS] 数据库名 [DEFAULT CHARSET 字符集] [COLLATE 排序规则];</code></li></ul></li><li>删除 <ul><li><code>DROP DATABSE [IF EXISTS] 数据库名</code></li></ul></li><li>使用 <ul><li><code>USE 数据库名</code></li></ul></li></ul><div class="language-shell vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">shell</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">mysql</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> -u</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> root</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> -p</span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> # 进入mysql</span></span></code></pre></div><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">SHOW DATABASES; # 展示所有数据库</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">CREATE</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> DATABASE</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> custom</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; # 创建一个名为custom的数据库</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">USE</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> custom; # 使用custom数据库</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">SELECT</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> DATABASE</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(); # 当前使用的是custom数据库</span></span></code></pre></div><h4 id="ddl-表操作" tabindex="-1">DDL - 表操作 <a class="header-anchor" href="#ddl-表操作" aria-label="Permalink to "DDL - 表操作""></a></h4><h5 id="创建表" tabindex="-1">创建表 <a class="header-anchor" href="#创建表" aria-label="Permalink to "创建表""></a></h5><p><strong>在命令行下，可以在多行内编写一个SQL语句</strong></p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">SHOW TABLES; # 查询当前数据库所有表</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">DESC</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 表名; # 查询 表结构</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">SHOW </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">CREATE</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> TABLE</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 表名; # 查询指定表的建表语句</span></span></code></pre></div><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"># 创建表</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">CREATE</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> TABLE</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> custom</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> param1 type1 [comment ''],</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> param2 type2 [comment ''],</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> param3 type3 [comment ''],</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> param4 type4 [comment '']</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)[comment '']</span></span></code></pre></div><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"># 创建一个tb_user表</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">create</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> tb_user</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> id </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">int</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'编号'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> name</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> varchar</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">50</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'姓名'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> age </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">int</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'年龄'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> gender </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">varchar</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'性别'</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> ) comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'用户表'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"># 展示数据库中所有表</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">show tables;</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"># 查询表内所有字段</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">desc</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> tb_user;</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"># 展示表的所有信息（包含字段注释、存储引擎、默认字符集、排序规则等信息）</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">show </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">create</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> tb_user;</span></span></code></pre></div><p>案例 - 员工信息表</p><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">create</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> emp</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> id </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">int</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'编号'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> workno </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">varchar</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">10</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'工号'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> name</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> varchar</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">10</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'姓名'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> gender </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">char</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'性别'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> age </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">tinyint</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> unsigned comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'年龄'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> idcard </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">char</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">18</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'身份证号'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> entrydate </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">date</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'入职时间'</span></span>
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<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'员工表'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span></code></pre></div><p>创建成功后，输入<code>desc emp</code>查看</p><div class="language-shell vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">shell</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">mysql</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">> </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">desc</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> emp</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
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<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">+-----------+------------------+------+-----+---------+-------+</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Field</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Type</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Null</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Key</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Default</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Extra</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span></span>
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<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">+-----------+------------------+------+-----+---------+-------+</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> id</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> int</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> YES</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> NULL</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> workno</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> varchar(10</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> YES</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> NULL</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span></span>
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<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> name</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> varchar(10</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> YES</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> NULL</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> gender</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> char(1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> YES</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> NULL</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span></span>
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||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> age</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> tinyint</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> unsigned</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> YES</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> NULL</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> idcard</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> char(18</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> YES</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> NULL</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">|</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> entrydate</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> date</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> YES</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> NULL</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span></span>
|
||
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">+-----------+------------------+------+-----+---------+-------+</span></span>
|
||
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">7</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> rows</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> in</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> set</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (0.00 </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">sec</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span></code></pre></div><h5 id="修改表" tabindex="-1">修改表 <a class="header-anchor" href="#修改表" aria-label="Permalink to "修改表""></a></h5><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"># 添加一个字段</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">alter</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 表名 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">add</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 字段名 类型(长度) [comment '']</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"># 修改一个字段</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">alter</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 表名 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">modify</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 旧字段名 新字段名 类型(长度) [comment '']</span></span>
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||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"># 删除一个字段</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">alter</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 表名 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">drop</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 字段名</span></span>
|
||
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"># 修改表名</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">alter</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 表名 rename </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">to</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> 新表名</span></span></code></pre></div><div class="language-sql vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">sql</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">alter</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> emp </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">add</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> nickname </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">varchar</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">20</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) comment </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'昵称'</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">alter</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> emp </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">modify</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> nickname username </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">varchar</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">30</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">alter</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> emp </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">drop</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> username</span></span>
|
||
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">alter</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> table</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> emp rename </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">to</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> employee</span></span></code></pre></div><h3 id="mysql数据类型" tabindex="-1">MySQL数据类型 <a class="header-anchor" href="#mysql数据类型" aria-label="Permalink to "MySQL数据类型""></a></h3><h4 id="数值类型" tabindex="-1">数值类型 <a class="header-anchor" href="#数值类型" aria-label="Permalink to "数值类型""></a></h4><p>在定义字段时，通过关键字<code>UNSIGNED</code>确定其<code>无符号 / 有符号</code></p><table tabindex="0"><thead><tr><th style="text-align:left;">类型</th><th style="text-align:left;">大小</th><th style="text-align:left;">范围（有符号）</th><th style="text-align:left;">范围（无符号）</th><th style="text-align:left;">用途</th></tr></thead><tbody><tr><td style="text-align:left;">TINYINT</td><td style="text-align:left;">1 Bytes</td><td style="text-align:left;">(-128，127)</td><td style="text-align:left;">(0，255)</td><td style="text-align:left;">小整数值</td></tr><tr><td style="text-align:left;">SMALLINT</td><td style="text-align:left;">2 Bytes</td><td style="text-align:left;">(-32 768，32 767)</td><td style="text-align:left;">(0，65 535)</td><td style="text-align:left;">大整数值</td></tr><tr><td style="text-align:left;">MEDIUMINT</td><td style="text-align:left;">3 Bytes</td><td style="text-align:left;">(-8 388 608，8 388 607)</td><td style="text-align:left;">(0，16 777 215)</td><td style="text-align:left;">大整数值</td></tr><tr><td style="text-align:left;">INT或INTEGER</td><td style="text-align:left;">4 Bytes</td><td style="text-align:left;">(-2 147 483 648，2 147 483 647)</td><td style="text-align:left;">(0，4 294 967 295)</td><td style="text-align:left;">大整数值</td></tr><tr><td style="text-align:left;">BIGINT</td><td style="text-align:left;">8 Bytes</td><td style="text-align:left;">(-9,223,372,036,854,775,808，9 223 372 036 854 775 807)</td><td style="text-align:left;">(0，18 446 744 073 709 551 615)</td><td style="text-align:left;">极大整数值</td></tr><tr><td style="text-align:left;">FLOAT</td><td style="text-align:left;">4 Bytes</td><td style="text-align:left;">(-3.402 823 466 E+38，-1.175 494 351 E-38)，0，(1.175 494 351 E-38，3.402 823 466 351 E+38)</td><td style="text-align:left;">0，(1.175 494 351 E-38，3.402 823 466 E+38)</td><td style="text-align:left;">单精度 浮点数值</td></tr><tr><td style="text-align:left;">DOUBLE</td><td style="text-align:left;">8 Bytes</td><td style="text-align:left;">(-1.797 693 134 862 315 7 E+308，-2.225 073 858 507 201 4 E-308)，0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308)</td><td style="text-align:left;">0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308)</td><td style="text-align:left;">双精度 浮点数值</td></tr><tr><td style="text-align:left;">DECIMAL</td><td style="text-align:left;">对DECIMAL(M,D) ，如果M>D，为M+2否则为D+2</td><td style="text-align:left;">依赖于M和D的值</td><td style="text-align:left;">依赖于M和D的值</td><td style="text-align:left;">小数值</td></tr></tbody></table><h4 id="字符串类型" tabindex="-1">字符串类型 <a class="header-anchor" href="#字符串类型" aria-label="Permalink to "字符串类型""></a></h4><table tabindex="0"><thead><tr><th style="text-align:left;">类型</th><th style="text-align:left;">大小</th><th style="text-align:left;">用途</th></tr></thead><tbody><tr><td style="text-align:left;">CHAR</td><td style="text-align:left;">0-255 bytes</td><td style="text-align:left;">定长字符串</td></tr><tr><td style="text-align:left;">VARCHAR</td><td style="text-align:left;">0-65535 bytes</td><td style="text-align:left;">变长字符串</td></tr><tr><td style="text-align:left;">TINYBLOB</td><td style="text-align:left;">0-255 bytes</td><td style="text-align:left;">不超过 255 个字符的二进制字符串</td></tr><tr><td style="text-align:left;">TINYTEXT</td><td style="text-align:left;">0-255 bytes</td><td style="text-align:left;">短文本字符串</td></tr><tr><td style="text-align:left;">BLOB</td><td style="text-align:left;">0-65 535 bytes</td><td style="text-align:left;">二进制形式的长文本数据</td></tr><tr><td style="text-align:left;">TEXT</td><td style="text-align:left;">0-65 535 bytes</td><td style="text-align:left;">长文本数据</td></tr><tr><td style="text-align:left;">MEDIUMBLOB</td><td style="text-align:left;">0-16 777 215 bytes</td><td style="text-align:left;">二进制形式的中等长度文本数据</td></tr><tr><td style="text-align:left;">MEDIUMTEXT</td><td style="text-align:left;">0-16 777 215 bytes</td><td style="text-align:left;">中等长度文本数据</td></tr><tr><td style="text-align:left;">LONGBLOB</td><td style="text-align:left;">0-4 294 967 295 bytes</td><td style="text-align:left;">二进制形式的极大文本数据</td></tr><tr><td style="text-align:left;">LONGTEXT</td><td style="text-align:left;">0-4 294 967 295 bytes</td><td style="text-align:left;">极大文本数据</td></tr></tbody></table><p><strong>注意</strong>：char(n) 和 varchar(n) 中括号中 n 代表字符的个数，并不代表字节个数，比如 CHAR(30) 就可以存储 30 个字符。</p><p>CHAR 和 VARCHAR 类型类似，但它们保存和检索的方式不同。它们的最大长度和是否尾部空格被保留等方面也不同。在存储或检索过程中不进行大小写转换。<strong>CHAR性能更优</strong></p><p>BINARY 和 VARBINARY 类似于 CHAR 和 VARCHAR，不同的是它们包含二进制字符串而不要非二进制字符串。也就是说，它们包含字节字符串而不是字符字符串。这说明它们没有字符集，并且排序和比较基于列值字节的数值值。</p><p>BLOB 是一个二进制大对象，可以容纳可变数量的数据。有 4 种 BLOB 类型：TINYBLOB、BLOB、MEDIUMBLOB 和 LONGBLOB。它们区别在于可容纳存储范围不同。</p><p>有 4 种 TEXT 类型：TINYTEXT、TEXT、MEDIUMTEXT 和 LONGTEXT。对应的这 4 种 BLOB 类型，可存储的最大长度不同，可根据实际情况选择。</p><h4 id="日期时间类型" tabindex="-1">日期时间类型 <a class="header-anchor" href="#日期时间类型" aria-label="Permalink to "日期时间类型""></a></h4><table tabindex="0"><thead><tr><th style="text-align:left;">类型</th><th style="text-align:left;">大小 ( bytes)</th><th style="text-align:left;">范围</th><th style="text-align:left;">格式</th><th style="text-align:left;">用途</th></tr></thead><tbody><tr><td style="text-align:left;">DATE</td><td style="text-align:left;">3</td><td style="text-align:left;">1000-01-01/9999-12-31</td><td style="text-align:left;">YYYY-MM-DD</td><td style="text-align:left;">日期值</td></tr><tr><td style="text-align:left;">TIME</td><td style="text-align:left;">3</td><td style="text-align:left;">'-838:59:59'/'838:59:59'</td><td style="text-align:left;">HH:MM:SS</td><td style="text-align:left;">时间值或持续时间</td></tr><tr><td style="text-align:left;">YEAR</td><td style="text-align:left;">1</td><td style="text-align:left;">1901/2155</td><td style="text-align:left;">YYYY</td><td style="text-align:left;">年份值</td></tr><tr><td style="text-align:left;">DATETIME</td><td style="text-align:left;">8</td><td style="text-align:left;">1000-01-01 00:00:00/9999-12-31 23:59:59</td><td style="text-align:left;">YYYY-MM-DD HH:MM:SS</td><td style="text-align:left;">混合日期和时间值</td></tr><tr><td style="text-align:left;">TIMESTAMP</td><td style="text-align:left;">4</td><td style="text-align:left;">1970-01-01 00:00:00/2038结束时间是第 <strong>2147483647</strong> 秒，北京时间 <strong>2038-1-19 11:14:07</strong>，格林尼治时间 2038年1月19日 凌晨 03:14:07</td><td style="text-align:left;">YYYYMMDD HHMMSS</td><td style="text-align:left;">混合日期和时间值，时间戳</td></tr></tbody></table></div></div></main><footer class="VPDocFooter" data-v-01a78eb7 data-v-46a899aa><!--[--><!--]--><div class="edit-info" data-v-46a899aa><div class="edit-link" data-v-46a899aa><a class="VPLink link vp-external-link-icon no-icon edit-link-button" href="https://github.com/ZiuChen/ZiuChen.github.io/edit/main/docs/note/MySQL.md" target="_blank" rel="noreferrer" data-v-46a899aa><!--[--><span class="vpi-square-pen edit-link-icon" data-v-46a899aa></span> Edit this page on GitHub<!--]--></a></div><div class="last-updated" data-v-46a899aa><p class="VPLastUpdated" data-v-46a899aa data-v-26673fa8>Updated Date: <time datetime="2024-06-07T03:35:23.000Z" data-v-26673fa8></time></p></div></div><nav class="prev-next" aria-labelledby="doc-footer-aria-label" data-v-46a899aa><span class="visually-hidden" id="doc-footer-aria-label" data-v-46a899aa>Pager</span><div class="pager" data-v-46a899aa><!----></div><div class="pager" 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