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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></header><div class="menu-tocs"><div class="menu-btn"><svg aria-hidden="true" fill="currentColor" height="1em" width="1em" viewBox="0 0 16 16" version="1.1" data-view-component="true">
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<path fill-rule="evenodd" d="M2 4a1 1 0 100-2 1 1 0 000 2zm3.75-1.5a.75.75 0 000 1.5h8.5a.75.75 0 000-1.5h-8.5zm0 5a.75.75 0 000 1.5h8.5a.75.75 0 000-1.5h-8.5zm0 5a.75.75 0 000 1.5h8.5a.75.75 0 000-1.5h-8.5zM3 8a1 1 0 11-2 0 1 1 0 012 0zm-1 6a1 1 0 100-2 1 1 0 000 2z"></path>
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</svg></div><div class="menu-modal"><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#入门">入门</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#介绍">介绍</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#登录mysql">登录MySQL</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#常用的">常用的</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#数据库-database">数据库 Database</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#表-table">表 Table</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#proccess">Proccess</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#查看-mysql-信息">查看 MySQL 信息</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#退出mysql会话">退出MySQL会话</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#备份">备份</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#mysql-示例">MySQL 示例</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#管理表格">管理表格</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#从表中查询数据">从表中查询数据</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#从多个表查询">从多个表查询</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#使用-sql-约束">使用 SQL 约束</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#修改数据">修改数据</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#管理视图">管理视图</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#管理触发器">管理触发器</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#when">WHEN</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#event">EVENT</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#trigger_type">TRIGGER_TYPE</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#管理索引">管理索引</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#mysql-数据类型">MySQL 数据类型</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#strings">Strings</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#date--time">Date & time</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#numeric">Numeric</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#另见">另见</a></div></div><div class="h1wrap-body"><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="入门"><a aria-hidden="true" tabindex="-1" href="#入门"><span class="icon icon-link"></span></a>入门</h2><div class="wrap-body">
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</svg></div><div class="menu-modal"><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#入门">入门</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#介绍">介绍</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#登录mysql">登录MySQL</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#常用的">常用的</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#数据库-database">数据库 Database</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#表-table">表 Table</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#proccess">Proccess</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#查看-mysql-信息">查看 MySQL 信息</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#退出mysql会话">退出MySQL会话</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#备份">备份</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#mysql-示例">MySQL 示例</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#管理表格">管理表格</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#从表中查询数据">从表中查询数据</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#从多个表查询">从多个表查询</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#使用-sql-约束">使用 SQL 约束</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#修改数据">修改数据</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#管理视图">管理视图</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#管理触发器">管理触发器</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#when">WHEN</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#event">EVENT</a><a aria-hidden="true" class="leve4 tocs-link" data-num="4" href="#trigger_type">TRIGGER_TYPE</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#管理索引">管理索引</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#mysql-数据类型">MySQL 数据类型</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#strings">Strings</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#date--time">Date & time</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#numeric">Numeric</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#函数">函数</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#聚合函数">聚合函数</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#数学函数">数学函数</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#日期和时间函数">日期和时间函数</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#字符串函数">字符串函数</a><a aria-hidden="true" class="leve3 tocs-link" data-num="3" href="#高级函数">高级函数</a><a aria-hidden="true" class="leve2 tocs-link" data-num="2" href="#另见">另见</a></div></div><div class="h1wrap-body"><div class="wrap h2body-exist"><div class="wrap-header h2wrap"><h2 id="入门"><a aria-hidden="true" tabindex="-1" href="#入门"><span class="icon icon-link"></span></a>入门</h2><div class="wrap-body">
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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">
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<!--rehype:wrap-class=row-span-3-->
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<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>
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<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>
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</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">
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</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">
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<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></tbody></table>
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</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">
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<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>
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</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">
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<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>
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</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">
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<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>
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</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">
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<!--rehype:wrap-class=col-span-3 -->
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<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>
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</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">
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<ul>
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||||
<li><a href="http://www.w3school.com.cn/sql/index.asp">SQL 基础教程</a> <em>(w3school.com.cn)</em></li>
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||||
|
||||
Reference in New Issue
Block a user