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<!DOCTYPE HTML>
<html lang="zh-CN">
<head><meta name="generator" content="Hexo 3.9.0">
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<meta name="description" content="1.MySQL概述1.1 数据库相关概念
名称
全称
简称
数据库
存储数据的仓库，数据是有组织的进行存储
DataBase（DB）
数据库管理系统
操纵和管理数据库的大型软件
DataBase Management Syst">
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<script>
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</script></head>
<div id="loading-container">
<p class="loading-text"></p>
<div class="loading-image">
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<h1 id="1-MySQL概述"><a href="#1-MySQL概述" class="headerlink" title="1.MySQL概述"></a>1.MySQL概述</h1><h2 id="1-1-数据库相关概念"><a href="#1-1-数据库相关概念" class="headerlink" title="1.1 数据库相关概念"></a>1.1 数据库相关概念</h2><table>
<thead>
<tr>
<th>名称</th>
<th>全称</th>
<th>简称</th>
</tr>
</thead>
<tbody><tr>
<td>数据库</td>
<td>存储数据的仓库，数据是有组织的进行存储</td>
<td>DataBase（DB）</td>
</tr>
<tr>
<td>数据库管理系统</td>
<td>操纵和管理数据库的大型软件</td>
<td>DataBase Management System (DBMS)</td>
</tr>
<tr>
<td>SQL</td>
<td>操作关系型数据库的编程语言，定义了一套操作 关系型数据库统一标准</td>
<td>Structured Query Language (SQL)</td>
</tr>
</tbody></table>
<h3 id="1-1-1mysql数据库连接"><a href="#1-1-1mysql数据库连接" class="headerlink" title="1.1.1mysql数据库连接"></a>1.1.1mysql数据库连接</h3><ol>
<li>使用MySQL提供的客户端命令行工具</li>
<li>使用系统自带的命令行工具执行指令</li>
</ol>
<pre><code>mysql [-h 127.0.0.1] [-P 3306] -u root -p
参数：
-h : MySQL服务所在的主机IP
-P : MySQL服务端口号， 默认3306
-u : MySQL数据库用户名
-p ： MySQL数据库用户名对应的密码</code></pre><p>[]内为可选参数，如果需要连接远程的MySQL，需要加上这两个参数来指定远程主机IP、端口，如果 连接本地的MySQL，则无需指定这两个参数。</p>
<h3 id="1-1-2-数据模型"><a href="#1-1-2-数据模型" class="headerlink" title="1.1.2 数据模型"></a>1.1.2 数据模型</h3><p>1). 关系型数据库（RDBMS） 概念：建立在关系模型基础上，由多张相互连接的二维表组成的数据库。 而所谓二维表，指的是由行和列组成的表，如下图（就类似于Excel表格数据，有表头、有列、有行， 还可以通过一列关联另外一个表格中的某一列数据）。MySQL、Oracle、DB2、 SQLServer这些都是属于关系型数据库，里面都是基于二维表存储数据的。简单说，基于二维表存储 数据的数据库就成为关系型数据库，不是基于二维表存储数据的数据库，就是非关系型数据库。</p>
<p><img src="/mysql-01/image-20230317200345320.png" alt="image-20230317200345320"></p>
<p>特点： A. 使用表存储数据，格式统一，便于维护。 </p>
<p> B. 使用SQL语言操作，标准统一，使用方便。</p>
<p>2). 数据模型 MySQL是关系型数据库，是基于二维表进行数据存储的，具体的结构图下:</p>
<p><img src="/mysql-01/image-20230317200415240.png" alt="image-20230317200415240"></p>
<p>可以通过MySQL客户端连接数据库管理系统DBMS，然后通过DBMS操作数据库。 </p>
<p>可以使用SQL语句，通过数据库管理系统操作数据库，以及操作数据库中的表结构及数据。 一个数据库服务器中可以创建多个数据库，一个数据库中也可以包含多张表，而一张表中又可以包 含多行记录。</p>
<h1 id="2-SQL"><a href="#2-SQL" class="headerlink" title="2.SQL"></a>2.SQL</h1><p>全称 Structured Query Language，结构化查询语言。操作关系型数据库的编程语言，定义了 一套操作关系型数据库统一标准 。</p>
<h2 id="2-1-SQL通用语法"><a href="#2-1-SQL通用语法" class="headerlink" title="2.1 SQL通用语法"></a>2.1 SQL通用语法</h2><ol>
<li>SQL语句可以单行或多行书写，以分号结尾。</li>
<li>SQL语句可以使用空格/缩进来增强语句的可读性。</li>
<li>MySQL数据库的SQL语句不区分大小写，关键字建议使用大写。</li>
<li>注释： 单行注释：– 注释内容 或 # 注释内容 多行注释：/* 注释内容 */</li>
</ol>
<h2 id="2-2-sql分类"><a href="#2-2-sql分类" class="headerlink" title="2.2 sql分类"></a>2.2 sql分类</h2><p>SQL语句，根据其功能，主要分为四类：DDL、DML、DQL、DCL。</p>
<table>
<thead>
<tr>
<th>分类</th>
<th>全称</th>
<th>说明</th>
</tr>
</thead>
<tbody><tr>
<td>DDL</td>
<td>Data Definition Language</td>
<td>数据定义语言，用来定义数据库对象(数据库，表， 字段)</td>
</tr>
<tr>
<td>DML</td>
<td>Data Manipulation Language</td>
<td>数据操作语言，用来对数据库表中的数据进行增删改</td>
</tr>
<tr>
<td>DQL</td>
<td>Data Query Language</td>
<td>数据查询语言，用来查询数据库中表的记录</td>
</tr>
<tr>
<td>DCL</td>
<td>Data Control Language</td>
<td>数据控制语言，用来创建数据库用户、控制数据库的 访问权限</td>
</tr>
</tbody></table>
<h2 id="2-3-DDL"><a href="#2-3-DDL" class="headerlink" title="2.3 DDL"></a>2.3 DDL</h2><p>Data Definition Language，数据定义语言，用来定义数据库对象(数据库，表，字段) 。</p>
<h3 id="2-3-1-数据库操作"><a href="#2-3-1-数据库操作" class="headerlink" title="2.3.1 数据库操作"></a>2.3.1 数据库操作</h3><p>1). 查询所有数据库</p>
<pre><code>show databases ;</code></pre><p>2). 查询当前数据库</p>
<pre><code>select database() ;</code></pre><p>3). 创建数据库</p>
<pre><code>create database [ if not exists ] 数据库名 [ default charset 字符集 ] [ collate 排序
规则 ] ;
</code></pre><p>在同一个数据库服务器中，不能创建两个名称相同的数据库，否则将会报错。</p>
<p>可以通过if not exists 参数来解决这个问题，数据库不存在, 则创建该数据库，如果存在，则不 创建。</p>
<pre><code>create database if not extists itcast;
</code></pre><p>B. 创建一个itheima数据库，并且指定字符集</p>
<pre><code>create database 数据库名称 default charset utf8mb4;</code></pre><p>4). 删除数据库</p>
<pre><code> drop database [ if exists ] 数据库名 ;
</code></pre><p>如果删除一个不存在的数据库，将会报错。此时，可以加上参数 if exists ，如果数据库存在，再 执行删除，否则不执行删除。</p>
<p>5). 切换数据库</p>
<pre><code>use 数据库名 ;</code></pre><p>要操作某一个数据库下的表时，就需要通过该指令，切换到对应的数据库下，否则是不能操作的。</p>
<h3 id="2-3-2-表操作"><a href="#2-3-2-表操作" class="headerlink" title="2.3.2 表操作"></a>2.3.2 表操作</h3><h4 id="2-3-2-1-表操作-查询创建"><a href="#2-3-2-1-表操作-查询创建" class="headerlink" title="2.3.2.1 表操作-查询创建"></a>2.3.2.1 表操作-查询创建</h4><p>1). 查询当前数据库所有表</p>
<pre><code>show tables;</code></pre><p>2). 查看指定表结构</p>
<pre><code>desc 表名 ;
</code></pre><p>3). 查询指定表的建表语句</p>
<pre><code>show create table 表名 ;</code></pre><p>4). 创建表结构</p>
<pre class="line-numbers language-mysql"><code class="language-mysql">CREATE TABLE 表名(
字段1 字段1类型 [ COMMENT 字段1注释 ],
字段2 字段2类型 [COMMENT 字段2注释 ],
字段3 字段3类型 [COMMENT 字段3注释 ],
......
字段n 字段n类型 [COMMENT 字段n注释 ]
) [ COMMENT 表注释 ] ;<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>注意: […] 内为可选参数，最后一个字段后面没有逗号</p>
<p>比如，创建一张表 tb_user ，对应的结构如下，那么建表语句为：</p>
<p><img src="/mysql-01/image-20230318122920257.png" alt="image-20230318122920257"></p>
<pre class="line-numbers language-mysql"><code class="language-mysql">create table tb_user(
id int comment '编号',
name varchar(50) comment '姓名',
age int comment '年龄',
gender varchar(1) comment '性别'
) comment '用户表';
<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<h4 id="2-3-2-2-表操作-数据类型"><a href="#2-3-2-2-表操作-数据类型" class="headerlink" title="2.3.2.2 表操作-数据类型"></a>2.3.2.2 表操作-数据类型</h4><p> MySQL中的数据类型有很多，主要分为三类：数值类型、字符串类型、日期时间类型。</p>
<p>1). 数值类型</p>
<table>
<thead>
<tr>
<th align="left">类型</th>
<th align="left">大小</th>
<th align="left">范围（有符号）</th>
<th align="left">范围（无符号）</th>
<th align="left">用途</th>
</tr>
</thead>
<tbody><tr>
<td align="left">TINYINT</td>
<td align="left">1 Bytes</td>
<td align="left">(-128，127)</td>
<td align="left">(0，255)</td>
<td align="left">小整数值</td>
</tr>
<tr>
<td align="left">SMALLINT</td>
<td align="left">2 Bytes</td>
<td align="left">(-32 768，32 767)</td>
<td align="left">(0，65 535)</td>
<td align="left">大整数值</td>
</tr>
<tr>
<td align="left">MEDIUMINT</td>
<td align="left">3 Bytes</td>
<td align="left">(-8 388 608，8 388 607)</td>
<td align="left">(0，16 777 215)</td>
<td align="left">大整数值</td>
</tr>
<tr>
<td align="left">INT或INTEGER</td>
<td align="left">4 Bytes</td>
<td align="left">(-2 147 483 648，2 147 483 647)</td>
<td align="left">(0，4 294 967 295)</td>
<td align="left">大整数值</td>
</tr>
<tr>
<td align="left">BIGINT</td>
<td align="left">8 Bytes</td>
<td align="left">(-9,223,372,036,854,775,808，9 223 372 036 854 775 807)</td>
<td align="left">(0，18 446 744 073 709 551 615)</td>
<td align="left">极大整数值</td>
</tr>
<tr>
<td align="left">FLOAT</td>
<td align="left">4 Bytes</td>
<td 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 align="left">0，(1.175 494 351 E-38，3.402 823 466 E+38)</td>
<td align="left">单精度 浮点数值</td>
</tr>
<tr>
<td align="left">DOUBLE</td>
<td align="left">8 Bytes</td>
<td 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 align="left">0，(2.225 073 858 507 201 4 E-308，1.797 693 134 862 315 7 E+308)</td>
<td align="left">双精度 浮点数值</td>
</tr>
<tr>
<td align="left">DECIMAL</td>
<td align="left">对DECIMAL(M,D) ，如果M>D，为M+2否则为D+2</td>
<td align="left">依赖于M和D的值</td>
<td align="left">依赖于M和D的值</td>
<td align="left">小数值</td>
</tr>
</tbody></table>
<pre><code>如:
1). 年龄字段 -- 不会出现负数, 而且人的年龄不会太大
age tinyint unsigned
2). 分数 -- 总分100分, 最多出现一位小数