MySQL简单查询详解-单表查询
MySQL简单查询详解-单表查询
作者：尹正杰
版权声明：原创作品，谢绝转载！否则将追究法律责任。
一.查询的执行路径
一条SQL查询语句的执行过程大致如下图所示：
1>.客户端和服务端通过mysql协议进行通信，mysql服务器通过某种客户端发送来的查询语句的时候，首先会去本地检验缓存是否命中，如果请求的SQL语句之前有本查询过，就会把之前的查询结果直接返回给用户（查询缓存的功能最少要满足三成以上才有意义，如果所有的查询都去用缓存且所有的SQL没有一次被命中的话就毫无意义啦。）；
2>.如果查询的SQL没有命中，就会将SQL的请求交给解析器进行解析操作。必要时在预处理器的配合下，解析器会生成一个解析树，这个解析树会有很多条执行路径去查询我们想要得到的SQL结果；
3>.如此多的执行路径就会交给查询优化器进行查询操作，查询优化器会选择资源开销最少的路径去执行SQL语句，与此同时，它还可能改写SQL语句，只要改写的结果和用户要查询的结果一致即可，查询优化器选择最优的一条执行路径之后又将这个结果交给查询执行计划进行排队（注意，MySQL的用户同时查询可能不止一个，因此并发的时候需要给它一个队列，哪些查询比较先进的会优先被查询到返回给用户）；
4>.以上的所有操作都没有执行的权限，最终执行查询操作的还是查询执行引擎。但是查询引擎并不能直接到磁盘上取数据，查询引擎本事只是把查询请求转换成对应表的存储引擎的API调用；
5>.我们知道存储引擎其实是表类型，存储引擎根据查询执行引擎的API调用从磁盘上获取对方所需要的数据并层层返回给用户，在返回的途中，mysql还要考虑是否将查询结果进行缓存操作。
二.选择和投影
1.投影和选择
投影其实就是挑选要符合的字段，选择就是挑选符合条件的行。
投影：select 字段1，字段2，... from tb_name;
常用语法格式：selcet * from tb_name;
选择：select 字段1，字段2,.... from tb_name where 子句（布尔条件表达式）;
2.布尔条件表达式操作符
= 等值比较
<=>：跟空值比较不会产生额外信息
<>:不等值
<:
<=
>
>=
IS NULL:是否为空
IS NOT NULL：是否不空
LIKE：支持的通配符%(任意长度的任意字符) _（任意单个字符）
RLIKE，REGEXP：支持使用正则表达式作为条件（注意LIKE和RLIKE都是用来做字符比较的，如果用来做数值比较的话性能就相当低了。）
IN：判断某行的某一字段的值是否在给定的列表中
BETWEEN...AND....:判断指定的值是否位于指定的范围之间（比如，判断一个数值在10和20之间，我们就可以这样写"X BETWEEN 10 AND 20"）
案例展示：
mysql> create table stars(SID int unsigned auto_increment not null unique key,Name char() not null,Age tinyint unsigned not null,Gender Enum('boy','girl') not null, Tearch char());
Query OK, rows affected (0.01 sec)
mysql>
mysql> desc stars;
+--------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------------------+------+-----+---------+----------------+
| SID | int() unsigned | NO | PRI | NULL | auto_increment |
| Name | char() | NO | | NULL | |
| Age | tinyint() unsigned | NO | | NULL | |
| Gender | enum('boy','girl') | NO | | NULL | |
| Tearch | char() | YES | | NULL | |
+--------+---------------------+------+-----+---------+----------------+
rows in set (0.00 sec)
mysql>
mysql> insert into stars values (,"sun wukong",,'boy','putilaozu'),(,'yinzhengjie',,'boy','himslef'),(,'liufei',,'boy','jia baoyu');
Query OK, rows affected (0.00 sec)
Records: Duplicates: Warnings:
mysql>
mysql> insert into stars values (,"han senyu",,'boy','cang laoshi'),(,'jia shanpeng',,'boy','ji laosi'),(,'wu zhiguang',,'boy','ma laoshi');
Query OK, rows affected (0.00 sec)
Records: Duplicates: Warnings:
mysql>
mysql> select * from stars;
+-----+--------------+-----+--------+-------------+
| SID | Name | Age | Gender | Tearch |
+-----+--------------+-----+--------+-------------+
| | sun wukong | | boy | putilaozu |
| | yinzhengjie | | boy | himslef |
| | liufei | | boy | jia baoyu |
| | han senyu | | boy | cang laoshi |
| | jia shanpeng | | boy | ji laosi |
| | wu zhiguang | | boy | ma laoshi |
+-----+--------------+-----+--------+-------------+
rows in set (0.00 sec)
mysql> select * from stars where Age between and ;
+-----+--------------+-----+--------+-------------+
| SID | Name | Age | Gender | Tearch |
+-----+--------------+-----+--------+-------------+
| | yinzhengjie | | boy | himslef |
| | han senyu | | boy | cang laoshi |
| | jia shanpeng | | boy | ji laosi |
+-----+--------------+-----+--------+-------------+
rows in set (0.00 sec)
mysql>
mysql> select Name,Age from stars where Age in (,);
+-------------+-----+
| Name | Age |
+-------------+-----+
| yinzhengjie | |
| liufei | |
| wu zhiguang | |
+-------------+-----+
rows in set (0.00 sec)
mysql>
mysql> select Name,Age from stars where Name rlike '^y.*';
+-------------+-----+
| Name | Age |
+-------------+-----+
| yinzhengjie | |
+-------------+-----+
row in set (0.00 sec)
mysql>
mysql> insert into stars values(,'jenny',,'girl','Li ming'),(,'danny',,'boy',NULL);
Query OK, rows affected (0.00 sec)
Records: Duplicates: Warnings:
mysql> select * from stars;
+-----+--------------+-----+--------+-------------+
| SID | Name | Age | Gender | Tearch |
+-----+--------------+-----+--------+-------------+
| | sun wukong | | boy | putilaozu |
| | yinzhengjie | | boy | himslef |
| | liufei | | boy | jia baoyu |
| | han senyu | | boy | cang laoshi |
| | jia shanpeng | | boy | ji laosi |
| | wu zhiguang | | boy | ma laoshi |
| | jenny | | girl | Li ming |
| | danny | | boy | NULL |
+-----+--------------+-----+--------+-------------+
rows in set (0.00 sec)
mysql>
mysql> select Name,Tearch from stars where Tearch is NULL;
+-------+--------+
| Name | Tearch |
+-------+--------+
| danny | NULL |
+-------+--------+
row in set (0.00 sec)
mysql> select Name,Tearch from stars where Tearch is NOT NULL;
+--------------+-------------+
| Name | Tearch |
+--------------+-------------+
| sun wukong | putilaozu |
| yinzhengjie | himslef |
| liufei | jia baoyu |
| han senyu | cang laoshi |
| jia shanpeng | ji laosi |
| wu zhiguang | ma laoshi |
| jenny | Li ming |
+--------------+-------------+
rows in set (0.00 sec)
mysql>
3.组合条件测试
NOT !
AND &&
OR ||
案例展示：
mysql> select database();
+-------------+
| database() |
+-------------+
| yinzhengjie |
+-------------+
row in set (0.00 sec) mysql> show tables;
+-----------------------+
| Tables_in_yinzhengjie |
+-----------------------+
| stars |
| t1 |
+-----------------------+
rows in set (0.01 sec) mysql>
mysql> select * from stars;
+-----+--------------+-----+--------+-------------+
| SID | Name | Age | Gender | Tearch |
+-----+--------------+-----+--------+-------------+
| | sun wukong | | boy | putilaozu |
| | yinzhengjie | | boy | himslef |
| | liufei | | boy | jia baoyu |
| | han senyu | | boy | cang laoshi |
| | jia shanpeng | | boy | ji laosi |
| | wu zhiguang | | boy | ma laoshi |
| | jenny | | girl | Li ming |
| | danny | | boy | NULL |
+-----+--------------+-----+--------+-------------+
rows in set (0.00 sec) mysql> select Name,Age from stars where Age > and Gender = 'boy';
+-------------+-----+
| Name | Age |
+-------------+-----+
| sun wukong | |
| yinzhengjie | |
| liufei | |
| han senyu | |
| wu zhiguang | |
+-------------+-----+
rows in set (0.00 sec) mysql>
4.排序
order by ‘排序字段’
默认为升序：ASC
降序：DESC
案例展示：
mysql> select * from stars;
+-----+--------------+-----+--------+-------------+
| SID | Name | Age | Gender | Tearch |
+-----+--------------+-----+--------+-------------+
| | sun wukong | | boy | putilaozu |
| | yinzhengjie | | boy | himslef |
| | liufei | | boy | jia baoyu |
| | han senyu | | boy | cang laoshi |
| | jia shanpeng | | boy | ji laosi |
| | wu zhiguang | | boy | ma laoshi |
| | jenny | | girl | Li ming |
| | danny | | boy | NULL |
+-----+--------------+-----+--------+-------------+
rows in set (0.00 sec) mysql>
mysql> select Name,Age from stars where Age > and Gender = 'boy' order by Name desc;
+-------------+-----+
| Name | Age |
+-------------+-----+
| yinzhengjie | |
| wu zhiguang | |
| sun wukong | |
| liufei | |
| han senyu | |
+-------------+-----+
rows in set (0.00 sec) mysql> select Name,Age from stars where Age > and Gender = 'boy' order by Name asc;
+-------------+-----+
| Name | Age |
+-------------+-----+
| han senyu | |
| liufei | |
| sun wukong | |
| wu zhiguang | |
| yinzhengjie | |
+-------------+-----+
rows in set (0.00 sec) mysql>
5.常用内置的聚合函数
关键字如下：
1>.SUM（）：运算和
2>.AVG（）：运算平均值
3>.MAX（）：运算最大值
5>.MIN（）：运算最小值
6>.COUNT（）：运算个数统计
案例展示：
mysql> select * from stars;
+-----+--------------+-----+--------+-------------+
| SID | Name | Age | Gender | Tearch |
+-----+--------------+-----+--------+-------------+
| | sun wukong | | boy | putilaozu |
| | yinzhengjie | | boy | himslef |
| | liufei | | boy | jia baoyu |
| | han senyu | | boy | cang laoshi |
| | jia shanpeng | | boy | ji laosi |
| | wu zhiguang | | boy | ma laoshi |
| | jenny | | girl | Li ming |
| | danny | | boy | NULL |
+-----+--------------+-----+--------+-------------+
rows in set (0.00 sec) mysql> select SUM(Age) from stars;
+----------+
| SUM(Age) |
+----------+
| |
+----------+
row in set (0.00 sec) mysql> select MAX(Age) from stars;
+----------+
| MAX(Age) |
+----------+
| |
+----------+
row in set (0.00 sec) mysql> select MIN(Age) from stars;
+----------+
| MIN(Age) |
+----------+
| |
+----------+
row in set (0.00 sec) mysql> select COUNT(Age) from stars;
+------------+
| COUNT(Age) |
+------------+
| |
+------------+
row in set (0.00 sec) mysql> select COUNT(*) from stars; #这种用法不建议，“*”的效率是非常低的，不如加入一个字段进去！
+----------+
| COUNT(*) |
+----------+
| |
+----------+
row in set (0.00 sec) mysql>
mysql> select SUM(Age) from stars where Age > ;
+----------+
| SUM(Age) |
+----------+
| |
+----------+
row in set (0.00 sec) mysql>
6.分组
关键字：group by
案例展示：
mysql> select * from stars;
+-----+--------------+-----+--------+-------------+
| SID | Name | Age | Gender | Tearch |
+-----+--------------+-----+--------+-------------+
| | sun wukong | | boy | putilaozu |
| | yinzhengjie | | boy | himslef |
| | liufei | | boy | jia baoyu |
| | han senyu | | boy | cang laoshi |
| | jia shanpeng | | boy | ji laosi |
| | wu zhiguang | | boy | ma laoshi |
| | jenny | | girl | Li ming |
| | danny | | boy | NULL |
+-----+--------------+-----+--------+-------------+
rows in set (0.00 sec) mysql>
mysql>
mysql> select Gender,SUM(Age) from stars group by Gender;
+--------+----------+
| Gender | SUM(Age) |
+--------+----------+
| boy | |
| girl | |
+--------+----------+
rows in set (0.00 sec) mysql>
7.对分组的条件过滤
关键字：having
案例展示：
mysql> select * from stars;
+-----+--------------+-----+--------+-------------+
| SID | Name | Age | Gender | Tearch |
+-----+--------------+-----+--------+-------------+
| | sun wukong | | boy | putilaozu |
| | yinzhengjie | | boy | himslef |
| | liufei | | boy | jia baoyu |
| | han senyu | | boy | cang laoshi |
| | jia shanpeng | | boy | ji laosi |
| | wu zhiguang | | boy | ma laoshi |
| | jenny | | girl | Li ming |
| | danny | | boy | NULL |
+-----+--------------+-----+--------+-------------+
rows in set (0.00 sec) mysql>
mysql> alter table stars add ClassID tinyint unsigned;
Query OK, rows affected (0.00 sec)
Records: Duplicates: Warnings: mysql>
mysql> select * from stars;
+-----+--------------+-----+--------+-------------+---------+
| SID | Name | Age | Gender | Tearch | ClassID |
+-----+--------------+-----+--------+-------------+---------+
| | sun wukong | | boy | putilaozu | NULL |
| | yinzhengjie | | boy | himslef | NULL |
| | liufei | | boy | jia baoyu | NULL |
| | han senyu | | boy | cang laoshi | NULL |
| | jia shanpeng | | boy | ji laosi | NULL |
| | wu zhiguang | | boy | ma laoshi | NULL |
| | jenny | | girl | Li ming | NULL |
| | danny | | boy | NULL | NULL |
+-----+--------------+-----+--------+-------------+---------+
rows in set (0.00 sec) mysql> update stars set ClassID = where SID = ;
Query OK, row affected (0.00 sec)
Rows matched: Changed: Warnings: mysql> update stars set ClassID = where SID = ;
Query OK, row affected (0.00 sec)
Rows matched: Changed: Warnings: mysql> update stars set ClassID = where SID = ;
Query OK, row affected (0.00 sec)
Rows matched: Changed: Warnings: mysql> update stars set ClassID = where SID = ;
Query OK, row affected (0.01 sec)
Rows matched: Changed: Warnings: mysql> update stars set ClassID = where SID = ;
Query OK, row affected (0.00 sec)
Rows matched: Changed: Warnings: mysql> update stars set ClassID = where SID = ;
Query OK, row affected (0.00 sec)
Rows matched: Changed: Warnings: mysql> update stars set ClassID = where SID = ;
Query OK, row affected (0.00 sec)
Rows matched: Changed: Warnings: mysql> update stars set ClassID = where SID = ;
Query OK, row affected (0.00 sec)
Rows matched: Changed: Warnings: mysql>
mysql> select * from stars;
+-----+--------------+-----+--------+-------------+---------+
| SID | Name | Age | Gender | Tearch | ClassID |
+-----+--------------+-----+--------+-------------+---------+
| | sun wukong | | boy | putilaozu | |
| | yinzhengjie | | boy | himslef | |
| | liufei | | boy | jia baoyu | |
| | han senyu | | boy | cang laoshi | |
| | jia shanpeng | | boy | ji laosi | |
| | wu zhiguang | | boy | ma laoshi | |
| | jenny | | girl | Li ming | |
| | danny | | boy | NULL | |
+-----+--------------+-----+--------+-------------+---------+
rows in set (0.00 sec) mysql>
mysql> select ClassID,Count(Name),sum(Age) from stars group by ClassID;
+---------+-------------+----------+
| ClassID | Count(Name) | sum(Age) |
+---------+-------------+----------+
| | | |
| | | |
| | | |
| | | |
| | | |
+---------+-------------+----------+
rows in set (0.00 sec) mysql>
mysql> select ClassID,Count(Name) from stars group by ClassID having Count(Name) >=;
+---------+-------------+
| ClassID | Count(Name) |
+---------+-------------+
| | |
| | |
+---------+-------------+
rows in set (0.00 sec) mysql>
mysql> select ClassID from stars group by ClassID having sum(Age) >=;
+---------+
| ClassID |
+---------+
| |
+---------+
row in set (0.00 sec) mysql>
8.只返回有用的行
关键字：LIMIT（一个数为显示的行数，两个数字为偏移第一个数字行，显示第二个数字）
案例展示：
mysql> select * from stars ;
+-----+--------------+-----+--------+-------------+---------+
| SID | Name | Age | Gender | Tearch | ClassID |
+-----+--------------+-----+--------+-------------+---------+
| | sun wukong | | boy | putilaozu | |
| | yinzhengjie | | boy | himslef | |
| | liufei | | boy | jia baoyu | |
| | han senyu | | boy | cang laoshi | |
| | jia shanpeng | | boy | ji laosi | |
| | wu zhiguang | | boy | ma laoshi | |
| | jenny | | girl | Li ming | |
| | danny | | boy | NULL | |
+-----+--------------+-----+--------+-------------+---------+
rows in set (0.00 sec) mysql>
mysql> select * from stars limit ;
+-----+-------------+-----+--------+-----------+---------+
| SID | Name | Age | Gender | Tearch | ClassID |
+-----+-------------+-----+--------+-----------+---------+
| | sun wukong | | boy | putilaozu | |
| | yinzhengjie | | boy | himslef | |
+-----+-------------+-----+--------+-----------+---------+
rows in set (0.00 sec) mysql> select * from stars limit ,;
+-----+--------------+-----+--------+-------------+---------+
| SID | Name | Age | Gender | Tearch | ClassID |
+-----+--------------+-----+--------+-------------+---------+
| | liufei | | boy | jia baoyu | |
| | han senyu | | boy | cang laoshi | |
| | jia shanpeng | | boy | ji laosi | |
+-----+--------------+-----+--------+-------------+---------+
rows in set (0.00 sec) mysql>
9.select语句的执行流程
from clause --> where clause --> group by --> having clause -->order by --> select -->limit
select常用的修饰符：
distinct 重复的只显示一次
SQL_CACHE 缓存查询结果
SQL_NO_CACHE 不缓存查询结果
10.小试牛刀
我比较喜欢看日本的一个动漫叫《火影忍者》，如果要存储一些人员信息的话，我们应该如何搞呢？请用多张表将下面表格的信息保存。相信这对大家来说应该都是小case，如果你忘记如何写SQL语句的话，可以参考：http://www.cnblogs.com/yinzhengjie/p/7862654.html
MySQL简单查询详解-单表查询的更多相关文章
- mysql查询操作之单表查询、多表查询、子查询
一.单表查询 单表查询的完整语法: .完整语法(语法级别关键字的排列顺序如下) select distinct 字段1,字段2,字段3,... from 库名.表名 where 约束条件 group ...
- MySQL数据库实验二：单表查询
实验二 单表查询 一.实验目的 理解SELECT语句的操作和基本使用方法. 二.实验环境 是MS SQL SERVER 2005的中文客户端. 三.实验示例 1.查询全体学生的姓名.学号.所在系. ...
- 不使用left-join等多表关联查询，只用单表查询和Java程序，简便实现“多表查询”效果
上次我们提到,不使用left-loin关联查询,可能是为了提高效率或者配置缓存,也可以简化一下sql语句的编写.只写单表查询,sql真得太简单了.问题是,查询多个表的数据还是非常需要的. 因此,存在这 ...
- Hibernate第十篇【Hibernate查询详解、分页查询】
前言 在Hibernate的第二篇中只是简单地说了Hibernate的几种查询方式-.到目前为止,我们都是使用一些简单的主键查询阿-使用HQL查询所有的数据-.本博文主要讲解Hibernate的查询操 ...
- MySQL常用查询命令（单表查询）
查询语法如下: select... from... where... group by... (having)... order by...; 顺序是from (从指定表中) where (具体条件) ...
- MySql语句常用命令整理---单表查询
初始化t_employee表 创建t_employee表 -- DROP TABLE IF EXISTS test; CREATE TABLE t_employee ( _id INTEGER PRI ...
- MySQL（九）之数据表的查询详解（SELECT语法）一
这一篇是MySQL中的重点也是相对于MySQL中比较难得地方,个人觉得要好好的去归类,并多去练一下题目.MySQL的查询也是在笔试中必有的题目.希望我的这篇博客能帮助到大家! 重感冒下的我,很难受!k ...
- mysql数据库之单表查询
单标查询 单表查询语句 关键字执行的优先级 简单查询 where约束 group by 聚合函数 HAVING过滤 order by 查询排序 LIMIT限制查询的记录数 使用正则表达式查询 单表查询 ...
- MySql（六）单表查询
十.单表查询 一.单表查询的语法 SELECT 字段1,字段2... FROM 表名 WHERE 条件 GROUP BY field HAVING 筛选 ORDER BY field LIMIT 限制 ...
随机推荐
- P问题，NP问题，NPC问题，NP-hard问题
1.P问题:一个问题能找到一个在多项式时间里解决他的算法 多项式时间(o(1),o(lgn),o(n的a次方)) 非多项式时间 o(a的n次方) o(n!) 2.NP问题:在多项式时间找不到问题的解 ...
- MongoDB的账户与权限管理及在Python与Java中的登录
本文主要介绍了MongoDB的账户新建,权限管理(简单的),以及在Python,Java和默认客户端中的登陆. 默认的MongoDB是没有账户权限管理的,也就是说,不需要密码即可登陆,即可拥有读写的权 ...
- java十年，需要学会的Java开发体系
阿里十年,只剩下这套Java开发体系了,链接:https://www.jianshu.com/p/ca6c4a73aac9
- 《unity 3D 游戏开发 第二版》宣雨松 分享 pdf下载
链接:https://pan.baidu.com/s/1LfRTGUmaE_lGdcmd6QiZkg 提取码:e2sn
- 深入理解docker信号机制以及dumb-init的使用
一.前言 ● 容器中部署的时候往往都是直接运行二进制文件或命令,这样对于容器的作用更加直观,但是也会出现新的问题,比如子进程的资源回收.释放.托管等,处理不好,便会成为可怕的僵尸进程 ● 本文主要讨论 ...
- python3【基础】-赋值与深浅拷贝
一.Python的变量及其存储 在高级语言中,变量是对内存及其地址的抽象.对于python而言,python的一切变量都是对象,变量的存储,采用了引用语义的方式,存储的只是一个变量的值所在的内存地址, ...
- 11.4 Daily Scrum
今天依旧是学习阶段,大家继续学习安卓的一些相关内容,并尝试将要用到的数据的API应用到程序中去. Today's tasks Tomorrow's tasks 丁辛 餐厅列表json/xml数据 ...
- Scrum Meeting day 1
第一次会议,在这一次的会议中,明确了任务目标,并将任务进行合理分配,并且规划了整个任务的初步计划. No_00:分工情况 姓名 分工 崔强 PM 杜正远 主力工程师 王嘉豪 主力工程师 ...
- 【MOOC EXP】Linux内核分析实验五报告
程涵 原创博客 <Linux内核分析>MOOC课程http://mooc.study.163.com/course/USTC-1000029000 分析system_call中断处理过程 ...
- 基于Struts2+Hibernate的朋友圈留言网站开发的质量属性
在课堂上我们了解了质量高于功能,质量属性是指影响质量的相关因素,是对质量的描述.现在我们对基于SSH的交友网站开发的质量属性可以从以下几个方向进行分析: (1)可用性: 当错误发生时,使用可用性战术进 ...