刘说成 mysql 学习笔记2-MySQL教程-爱易网页

刘说成 mysql 学习笔记2

日期：2014-05-16　浏览次数：21286 次
刘道成 mysql 学习笔记2
仿ecshop建库

create database mugua charset utf8;

use mugua;

create table goods(
goods_id int primary key auto_increment,
cat_id smallint not null default 0,
goods_sn char(15) not null default '',
goods_name varchar(30) not null default '',
click_count mediumint unsigned not null default 0,
brand_id smallint not null default 0,
goods_number smallint not null default 0,
marcket_price decimal(7,2) not null default 0.00,
shop_price decimal(7,2) not null default 0.00,
add_time int unsigned not null default 0 
)charset utf8;

从一个数据库导数据到另一个数据库的方法
会碰到中文出现乱码   先运行这个语句 set names gbk
insert into mugua.goods
select
goods_id,cat_id,goods_sn,goods_name,click_count,
brand_id,goods_number,market_price,shop_price,add_time
from shop.goods;


create table category(
cat_id smallint primary key auto_increment,
cat_name varchar(30) not null default '',
parent_id smallint not null default 0
)charset utf8;

insert into mugua.category
select
cat_id,cat_name,parent_id
from shop.category;

create table brand(

brand_id smallint primary key auto_increment,
brand_name varchar(30) not null default''
)charset utf8;

insert into mugua.brand
select
brand_id,brand_name
from shop.brand;

（一）where  表达式在哪一（几）行成立  就把那一（几）行取出来
  select * from goods where cat_id=3;
  select * from goods where cat_id !=3;
等价于
 select * from goods where cat_id <>3;
 select * from goods where cat_id>3;
 select * from goods where cat_id<3;
 select * from goods where cat_id>=3;
 select * from goods where cat_id<=3;
 select * from goods where cat_id  in(3,4);
 select * from goods where cat_id between 3 and 5;
 select * from goods where cat_id >3 or cat_id <=2;
 select * from goods where cat_id>=3 and cat_id<=6;

（二）group by  分组查询
   group by 与max  min  sum  avg  count连用
1 查出最贵商品价格
select max(shop_price) from goods;
2 查出最便宜商品价格
select min(shop_price) from goods;
3 查出商品总量
select sum(goods_number) from goods;
4 查出所有商品平均价格
select avg(shop_price) from goods;
5,查出所有商品总类
select count(goods_id) from goods;

#查询每个栏目下  要用到group by
1 查出最贵商品价格
select cat_id,max(shop_price) from goods group by cat_id;

2 查出最便宜商品价格
select cat_id,min(shop_price) from goods group by cat_id;
3 查出商品总量
select cat_id,sum(goods_number) from goods group by cat_id;
4 查出所有商品平均价格
select cat_id,avg(shop_price) from goods group by cat_id;
5,查出所有商品总类
select cat_id,count(goods_id) from goods group by cat_id;

#把列名当变量就可以进行运算了  可以写出更加高效的sql语句

#查询每个栏目下积压的货款
select cat_id,sum(shop_price*goods_number) from goods group by cat_id;
#查询出每个商品比市场价低多少
select goods_id,goods_name,marcket_price-shop_price as cha from goods;

（三）having查询
where 发挥作用的时间在查表结果之前  
having 是筛选  是对查询结果的进一步选择
1，查询比市场价省200元以上得物品价格以及所省的钱

select goods_name,goods_id,marcket_price-shop_price as sheng from goods having sheng>200;
如果写成 
select goods_name,goods_id,marcket_price-shop_price as sheng from goods where sheng>200;
是错误的

当然也可以写成

select goods_name,goods_id,marcket_price-shop_price as sheng from goods where marcket_price-shop_price>200;

只不错计算了两次  不如having 好


2，查询积压货款超过 20000元货款的栏目 以及该货款

select cat_id,sum(shop_price*goods_number) as jiya from goods group by cat_id having jiya>20000;

更多资源  http://www.taobtbw.com/
（四）order by 和limit查询
1，按价格由高到低排序
select goods_name,goods_id,shop_price from goods order by shop_price desc; 
2，按发布时间由早到晚排序
select goods_id,goods_name,add_time from goods order by add_time;

3，按栏目由低到高排序，栏目内部按价格由高到低排序

select goods_id,goods_name,cat_id,shop_price from goods order by cat_id asc,shop_price desc;

limit 的用法  limit在语句的最后  起到限制的作用
limit[offset]N
offset :偏移量
N;去处的条目数量
offset不写则相当于 limit 0，N
是从0 开始算的  而不是1

4,取出价格最高的前三名商品

select goods_id,goods_name,shop_price from goods order by shop_price desc limit 0,3;

5,取出点击量前三名到前5名的商品
select goods_id,goods_name,click_count from goods order by click_count desc limit 2,3;

思考题  ：取出每个栏目下最贵的商品
错误1：select goods_id,goods_name,cat_id,max(shop_price) from goods group by cat_id  错误原因是用了聚合函数  而其他栏目以第一次遇到的为准

错误2： selec


                        <div class="clearfix"></div>
                    </div>
                    <nav aria-label="...">
                        <ul class="pager">
                            <li class="previous"><a href="44373">上一篇：MYSQL锁处理</a></li>

                            <li class="next"><a href="41355">下一篇： java联接mysql示例代码 </a></li>
                        </ul>
                    </nav>


                    <div class="alert alert-warning" role="alert">
                        <strong>免责声明：</strong> 本文仅代表作者个人观点，与爱易网无关。其原创性以及文中陈述文字和内容未经本站证实，对本文以及其中全部或者部分内容、文字的真实性、完整性、及时性本站不作任何保证或承诺，请读者仅作参考，并请自行核实相关内容。
                    </div>

                    

<div class="panel panel-default">
    <div class="panel-heading">
        <h3 class="panel-title">相关资料<span><a target="_blank" class="pull-right" href="/MYSQL/">更多></a></span></h3>
    </div>
    <div class="panel-body row">
        <ol>

            
                  <div class="col-md-6 col-xs-12">
                      <li class="articleAbout"><a href='/MYSQL/35656' title=' MYSQL Merge跟分区 ' target="_blank">
                         MYSQL Merge跟分区 </a></li></div>
                   
                
                  <div class="col-md-6 col-xs-12">
                      <li class="articleAbout"><a href='/MYSQL/42308' title=' mysql 怎么高效批量插入记录 ' target="_blank">
                         mysql 怎么高效批量插入记录 </a></li></div>
                   
                
                  <div class="col-md-6 col-xs-12">
                      <li class="articleAbout"><a href='/MYSQL/42548' title=' row_count()用mysql_affected_rows()获取后值一直为-1,该如何处理 ' target="_blank">
                         row_count()用mysql_affected_rows()获取后值一直为-1,该如何处理 </a></li></div>
                   
                
                  <div class="col-md-6 col-xs-12">
                      <li class="articleAbout"><a href='/MYSQL/41087' title=' MySql中delimiter的功用 ' target="_blank">
                         MySql中delimiter的功用 </a></li></div>
                   
                
                  <div class="col-md-6 col-xs-12">
                      <li class="articleAbout"><a href='/MYSQL/38029' title=' Spring联接MySQL、Oracle和SQL Server ' target="_blank">
                         Spring联接MySQL、Oracle和SQL Server </a></li></div>
                   
                
                  <div class="col-md-6 col-xs-12">
                      <li class="articleAbout"><a href='/MYSQL/38342' title=' 关于Linux系统上遇到的MySql有关问题，求指导 ' target="_blank">
                         关于Linux系统上遇到的MySql有关问题，求指导 </a></li></div>
                   
                
                  <div class="col-md-6 col-xs-12">
                      <li class="articleAbout"><a href='/MYSQL/37619' title=' Hibernate的MYSQL序列有关问题 ' target="_blank">
                         Hibernate的MYSQL序列有关问题 </a></li></div>
                   
                
                  <div class="col-md-6 col-xs-12">
                      <li class="articleAbout"><a href='/MYSQL/40484' title=' Mysql 官方Memcached 插件初始试用感受 ' target="_blank">
                         Mysql 官方Memcached 插件初始试用感受 </a></li></div>
                   
                
                  <div class="col-md-6 col-xs-12">
                      <li class="articleAbout"><a href='/MYSQL/42926' title=' 怎么实现like in结合，类似regexp_like ' target="_blank">
                         怎么实现like in结合，类似regexp_like </a></li></div>
                   
                
        </ol>
    </div>
</div>


                </div>

                <div class="col-lg-4 hidden-sm hidden-xs">
                    <!--右边的内容-->
                    <a id="AdPageRight1_AdPageRight" href="http://www.tdyun.com/cloud/?aiyiweb" target="_blank"><img class="img-responsive" src="/images/TdPageAd/vps1.png" alt="香港云服务器 免备案 云主机VPS 国内 独立IP 独享15M 月付SSD" /></a>

                    <script src='/Scripts/AdContentPage300_1.js' language='javascript'></script>
                    <script src='/Scripts/AdContentPage300_2.js' language='javascript'></script>
                    <script src='/Scripts/AdContentPage300_3.js' language='javascript'></script>
                    
<div class="panel panel-default">
      <div class="panel-heading">
        <h3 class="panel-title">推荐阅读<span><a target="_blank" class="pull-right" href="/MYSQL/">更多></a></span></h3>
      </div>
      <div class="panel-body">
          <ol>
        
                       <li class="articleAbout"><a href=/MYSQL/44066  title=' PostgreSQL 8.4.3 怎么导入一下uuid-ossp.sql ' target="_blank">
                             PostgreSQL 8.4.3 怎么导入一下uuid-ossp.sql </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/41431  title=' 用MySQL-Proxy兑现读写分离【转】 ' target="_blank">
                             用MySQL-Proxy兑现读写分离【转】 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/35753  title=' mysql 目录建立规则 ' target="_blank">
                             mysql 目录建立规则 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/43502  title=' 这样一个SQL语言有其他写法吗?该怎么解决 ' target="_blank">
                             这样一个SQL语言有其他写法吗?该怎么解决 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/38979  title=' mysql 外键容许为null or 空 ' target="_blank">
                             mysql 外键容许为null or 空 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/37552  title=' hibernate 连结 MYSQL联接字符串中的转义符 ' target="_blank">
                             hibernate 连结 MYSQL联接字符串中的转义符 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/36326  title=' MySQL中在带有GROUP BY的SELECT语句中显示COUNT()为0的结果 ' target="_blank">
                             MySQL中在带有GROUP BY的SELECT语句中显示COUNT()为0的结果 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/39608  title=' mysql游标有关问题 ' target="_blank">
                             mysql游标有关问题 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/40184  title=' mysqld_multi 配备MySQL多实例 ' target="_blank">
                             mysqld_multi 配备MySQL多实例 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/42344  title=' pgsql中if的小疑点 ' target="_blank">
                             pgsql中if的小疑点 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/44260  title=' mysql存储过程中怎么把查询的值取出来并赋给自己定义的字段 ' target="_blank">
                             mysql存储过程中怎么把查询的值取出来并赋给自己定义的字段 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/43770  title=' MySQL中连接不了，出现host 'localhost' is not allowed to connect to this MySQL server,该如何解决 ' target="_blank">
                             MySQL中连接不了，出现host 'localhost' is not allowed to connect to this MySQL server,该如何解决 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/41917  title=' 各位大侠们好,小弟的触发器总是报错，帮忙看看吧，多谢啦 ' target="_blank">
                             各位大侠们好,小弟的触发器总是报错，帮忙看看吧，多谢啦 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/41216  title=' mysql远程连接忽然变慢 ' target="_blank">
                             mysql远程连接忽然变慢 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/42438  title=' mysql怎么显示出现错误的表？如何修复全部错误表 ' target="_blank">
                             mysql怎么显示出现错误的表？如何修复全部错误表 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/42476  title=' 问：怎么MySql GUI tools备份数据库 ' target="_blank">
                             问：怎么MySql GUI tools备份数据库 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/38019  title=' JNDI tomcat6 配备Mysql的数据池 ' target="_blank">
                             JNDI tomcat6 配备Mysql的数据池 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/43232  title=' 一非常奇怪的有关问题（急） ' target="_blank">
                             一非常奇怪的有关问题（急） </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/38076  title=' 一个DDL导致MySQL主从停止有关问题及解决 ' target="_blank">
                             一个DDL导致MySQL主从停止有关问题及解决 </a></li>
                    
                       <li class="articleAbout"><a href=/MYSQL/36668  title=' MySQL：在命令行下创建 MySQL 存储过程有关问题 ' target="_blank">
                             MySQL：在命令行下创建 MySQL 存储过程有关问题 </a></li>
                    
            </ol>
      </div>
</div>

                </div>
            </div>
            <div class="clearfix"></div>

            
    <footer class=" footer navbar-bottom">
<em>友情链接：</em>
    
      <a href="http://www.aiyiweb.com/" target="_blank">爱易网 </a>            
    
      <a href="http://www.aiyiweb.com/" target="_blank">云虚拟主机技术 </a>            
    
      <a href="http://www.aiyiweb.com/" target="_blank">云服务器技术 </a>            
    
      <a href="http://www.aiyiweb.com/" target="_blank">程序设计技术 </a>            
    
      <a href="http://www.aiyiweb.com/" target="_blank">开发网站 </a>            
    
      <a href="http://www.aiyiweb.com/" target="_blank">APP开发教程 </a>            
    
<br />
<script type="text/javascript">(function(){document.write(unescape('%3Cdiv id="bdcs"%3E%3C/div%3E'));var bdcs = document.createElement('script');bdcs.type = 'text/javascript';bdcs.async = true;bdcs.src = 'http://znsv.baidu.com/customer_search/api/js?sid=15239353030108964139' + '&plate_url=' + encodeURIComponent(window.location.href) + '&t=' + Math.ceil(new Date()/3600000);var s = document.getElementsByTagName('script')[0];s.parentNode.insertBefore(bdcs, s);})();</script>


 

Copyright © 2013-2026 爱易网页 当前在线：231人　
        网站在10时28分4秒内访问总人数：68466人
    当前 15.90%
　<a href="https://beian.miit.gov.cn" target="_blank">粤ICP备18100884号-2 </a>
<script charset="UTF-8" id="LA_COLLECT" src="//sdk.51.la/js-sdk-pro.min.js"></script>
<script>LA.init({ id: "JszEmKrtpbU59dY5", ck: "JszEmKrtpbU59dY5" })</script>




</footer>


        </div>
   
</body>
</html>