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Java基础学习笔记二十五 MySQL

2024-11-01 16:27:39   213人阅读

MySQL

在dos中操作mysql

连接mysql命令： mysql -uroot -p密码 ，连接OK，会出现mysql>

对数据库的操作

创建一个库

create database 库名create database 库名 character set 编码
mysql> create database mybase;Query OK, 1 row affected (0.00 sec)mysql> show databases;+--------------------+| Database           |+--------------------+| information_schema || mybase             || mysql              || performance_schema || test               |+--------------------+5 rows in set (0.00 sec)

创建带有编码的

create database mybase01 character set gbk;
mysql> create database mybase01 character set gbk;Query OK, 1 row affected (0.00 sec)mysql> show databases;+--------------------+| Database           |+--------------------+| information_schema || mybase             || mybase01           || mysql              || performance_schema || test               |+--------------------+6 rows in set (0.00 sec)

查看编码：

mysql> show create database mybase01;+----------+------------------------------------------------------------------+| Database | Create Database                                                  |+----------+------------------------------------------------------------------+| mybase01 | CREATE DATABASE `mybase01` /*!40100 DEFAULT CHARACTER SET gbk */ |+----------+------------------------------------------------------------------+1 row in set (0.00 sec)

 查看数据库

mysql> show databases;+--------------------+| Database           |+--------------------+| information_schema || mybase             || mysql              || performance_schema || test               |+--------------------+5 rows in set (0.00 sec)

删除一个库

drop database 库名
mysql> drop database mybase;Query OK, 0 rows affected (0.00 sec)mysql> show databases;+--------------------+| Database           |+--------------------+| information_schema || mysql              || performance_schema || test               |+--------------------+4 rows in set (0.00 sec)

使用库  use 库名 

mysql> use mybaseDatabase changed

查看当前正在操作的库  select database(); 

mysql> select database();+------------+| database() |+------------+| mybase     |+------------+1 row in set (0.00 sec)

对数据库表的操作

创建一张表

 创建数据表的格式      create table 表名(       列名1 数据类型 约束,       列名2 数据类型 约束,       列名3 数据类型 约束      );
/*      创建用户表,用户编号,姓名,用户的地址      将编号列,设置为主键约束,保证列的数据唯一性,非空性      primary key AUTO_INCREMENT      让主键列数据,实现自动增长*/ CREATE TABLE users (     uid INT PRIMARY KEY AUTO_INCREMENT ,     uname VARCHAR(20),     uaddress VARCHAR(200) );
mysql>  CREATE TABLE users (    ->      uid INT PRIMARY KEY AUTO_INCREMENT ,    ->      uname VARCHAR(20),    ->      uaddress VARCHAR(200)    ->  );Query OK, 0 rows affected (0.02 sec)

查看数据库表  show tables; 

mysql> show tables;+------------------+| Tables_in_mybase |+------------------+| users            |+------------------+1 row in set (0.00 sec)

查看表的结构  desc 表名 

mysql> desc users;+----------+--------------+------+-----+---------+----------------+| Field    | Type         | Null | Key | Default | Extra          |+----------+--------------+------+-----+---------+----------------+| uid      | int(11)      | NO   | PRI | NULL    | auto_increment || uname    | varchar(20)  | YES  |     | NULL    |                || uaddress | varchar(200) | YES  |     | NULL    |                |+----------+--------------+------+-----+---------+----------------+3 rows in set (0.00 sec)

删除一张表  drop table 表名 

mysql> drop table users； Query OK, 0 rows affected (0.00 sec)mysql> show tables;Empty set (0.00 sec)

修改表

添加一列  alter table 表名 add 字段名 类型(长度) [约束] 

mysql> alter table users add tel int;Query OK, 0 rows affected (0.00 sec)Records: 0  Duplicates: 0  Warnings: 0
mysql> desc users ;+----------+--------------+------+-----+---------+----------------+| Field    | Type         | Null | Key | Default | Extra          |+----------+--------------+------+-----+---------+----------------+| uid      | int(11)      | NO   | PRI | NULL    | auto_increment || uname    | varchar(20)  | YES  |     | NULL    |                || uaddress | varchar(200) | YES  |     | NULL    |                || tel      | int(11)      | YES  |     | NULL    |                |+----------+--------------+------+-----+---------+----------------+4 rows in set (0.01 sec)

修改列的类型(长度、约束)  alter table 表名 modify 要修改的字段名 类型(长度) [约束] 

mysql> alter table users modify tel varchar(50);Query OK, 0 rows affected (0.27 sec)Records: 0  Duplicates: 0  Warnings: 0

修改列的列名  alter table 表名 change 旧列名 新列名 数据类型 约束 

mysql> alter table users change tel newtel double;Query OK, 0 rows affected (0.01 sec)Records: 0  Duplicates: 0  Warnings: 0
mysql> desc users ;+----------+--------------+------+-----+---------+----------------+| Field    | Type         | Null | Key | Default | Extra          |+----------+--------------+------+-----+---------+----------------+| uid      | int(11)      | NO   | PRI | NULL    | auto_increment || uname    | varchar(20)  | YES  |     | NULL    |                || uaddress | varchar(200) | YES  |     | NULL    |                || newtel   | double       | YES  |     | NULL    |                |+----------+--------------+------+-----+---------+----------------+4 rows in set (0.00 sec)

删除表的列  alter table 表名 drop 列名 

mysql> alter table users drop newtel;Query OK, 0 rows affected (0.02 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> desc users;+----------+--------------+------+-----+---------+----------------+| Field    | Type         | Null | Key | Default | Extra          |+----------+--------------+------+-----+---------+----------------+| uid      | int(11)      | NO   | PRI | NULL    | auto_increment || uname    | varchar(20)  | YES  |     | NULL    |                || uaddress | varchar(200) | YES  |     | NULL    |                |+----------+--------------+------+-----+---------+----------------+3 rows in set (0.00 sec)

修改表名  rename table 表名 to 新表名 

mysql> rename table users to newusers;Query OK, 0 rows affected (0.01 sec)mysql> show tables;+------------------+| Tables_in_mybase |+------------------+| newusers         |+------------------+1 row in set (0.00 sec)

查看表的字符集编码  show create table newusers; 

mysql> show create table newusers;+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| Table    | Create Table                                                       |+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| newusers | CREATE TABLE `newusers` (  `uid` int(11) NOT NULL AUTO_INCREMENT,  `uname` varchar(20) DEFAULT NULL,  `uaddress` varchar(200) DEFAULT NULL,  PRIMARY KEY (`uid`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 |+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+1 row in set (0.00 sec)

修改表的字符集  alter table 表名 character set 编码 

mysql> alter table newusers character set gbk;Query OK, 0 rows affected (0.03 sec)Records: 0  Duplicates: 0  Warnings: 0mysql> show create table newusers;+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| Table    | Create Table            |+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+| newusers | CREATE TABLE `newusers` (  `uid` int(11) NOT NULL AUTO_INCREMENT,  `uname` varchar(20) CHARACTER SET utf8 DEFAULT NULL,  `uaddress` varchar(200) CHARACTER SET utf8 DEFAULT NULL,  PRIMARY KEY (`uid`)) ENGINE=InnoDB DEFAULT CHARSET=gbk |+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+1 row in set (0.00 sec)

对数据库表记录进行操作(修改)

插入记录

insert into 表名(列名1,列名2,列名3……) values(值1,值2,值3……)insert into 表名 values(值1,值2,值3……)
insert into 表名 (列名1,列名2,列名3) values (值1,值2,值3),(值1,值2,值3)

先创建product表，然后添加数据。

CREATE TABLE product(   -- 主键列,自动增长   id INT PRIMARY KEY AUTO_INCREMENT,   -- 商品名字,可变字符,非空   pname VARCHAR(100) NOT NULL,   -- 商品的价格,double   price DOUBLE);
mysql> INSERT INTO product (id,pname,price) VALUES (1,‘笔记本‘,5555.99);ERROR 1366 (HY000): Incorrect string value: ‘\xB1\xCA\xBC\xC7\xB1\xBE‘ for column ‘pname‘ at row 1mysql> INSERT INTO product (id,pname,price) VALUES (2,‘智能手机‘,9999);ERROR 1366 (HY000): Incorrect string value: ‘\xD6\xC7\xC4\xDC\xCA\xD6...‘ for column ‘pname‘ at row 1mysql> INSERT INTO product (id,pname,price) VALUES (1,‘computer‘,5555.99);Query OK, 1 row affected (0.00 sec)mysql> INSERT INTO product (id,pname,price) VALUES (1,‘phone‘,5555.99);ERROR 1062 (23000): Duplicate entry ‘1‘ for key ‘PRIMARY‘mysql> INSERT INTO product (id,pname,price) VALUES (2,‘phone‘,5555.99);Query OK, 1 row affected (0.00 sec)

插入数据中文乱码问题解决办法

乱码原因：客户端和服务器之间传递字符的编码规则不一样。

方式一：直接修改数据库安装目录里面的my.ini文件的第57行【不建议】
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方式二： set names gbk; 

mysql> set names gbk;Query OK, 0 rows affected (0.00 sec)

再次插入中文，可以看到，不报错了。

mysql> INSERT INTO product (id,pname,price) VALUES (3,‘笔记本‘,5555.99);Query OK, 1 row affected (0.00 sec)mysql> INSERT INTO product (id,pname,price) VALUES (4,‘智能手机‘,9999);Query OK, 1 row affected (0.00 sec)

添加数据格式,不考虑主键  insert into 表名 (列名) values (值) 

mysql> INSERT INTO product (pname,price) VALUES(‘洗衣机‘,800);Query OK, 1 row affected (0.00 sec)

添加数据格式,所有值全给出  insert into 表名 values (全列值) 

mysql> INSERT INTO product VALUES (6,‘微波炉‘,300.25);Query OK, 1 row affected (0.00 sec)

添加数据格式,批量写入  insert into 表名 (列名1,列名2,列名3) values (值1,值2,值3),(值1,值2,值3) 

mysql> INSERT INTO product (pname,price) VALUES    -> (‘智能机器人‘,25999.22),    -> (‘彩色电视‘,1250.36),    -> (‘沙发‘,5899.02);Query OK, 3 rows affected (0.00 sec)Records: 3  Duplicates: 0  Warnings: 0

修改表记录

先看看表中的所有数据：

mysql> select * from product;+----+------------+----------+| id | pname      | price    |+----+------------+----------+|  1 | computer   |  5555.99 ||  2 | phone      |  5555.99 ||  3 | 笔记本         |  5555.99 ||  4 | 智能手机          |     9999 ||  5 | 洗衣机         |      800 ||  6 | 微波炉         |   300.25 ||  7 | 智能机器人          | 25999.22 ||  8 | 彩色电视          |  1250.36 ||  9 | 沙发          |  5899.02 |+----+------------+----------+9 rows in set (0.00 sec)

带条件的  update 表名 set字段名=值, 字段名=值, 字段名=值…… where 条件 

-- 修改智能手机,价格上调到15999mysql> UPDATE product SET price = 15999 WHERE id=2;Query OK, 1 row affected (0.00 sec)Rows matched: 1  Changed: 1  Warnings: 0
-- 修改彩色电视,名字改为黑白电视机,价格,100mysql> UPDATE product SET pname=‘黑白电视机‘, price=100 WHERE id = 6;Query OK, 1 row affected (0.00 sec)Rows matched: 1  Changed: 1  Warnings: 0
 修改条件的写法    id=6    id<>6    id<=6      与或非  && || !    && and    || or     ! not        id in (1,3,4,5,6) 包含
-- 将笔记本的价格,和空调的价格,全部修改为2000UPDATE product SET price = 2000 WHERE id = 1 OR id = 7;

不带条件的，它会将该列的所有记录都更改   update 表名 set 字段名=值, 字段名=值, 字段名=值……  

mysql> update product set price=999.999;Query OK, 9 rows affected (0.01 sec)Rows matched: 9  Changed: 9  Warnings: 0

删除表记录

带条件的  delete from 表名 where 条件 

不带条件的，会删除该表的所有记录  delete from 表名; 

-- 删除热水器DELETE FROM product WHERE id=8;

delete与truncate的区别

  • delete删除的时候是一条一条的删除记录，它配合事务，可以将删除的数据找回。
  • truncate删除，它是将整个表摧毁，然后再创建一张一模一样的表。它删除的数据无法找回。

Delete操作演示： 

mysql> start transaction;Query OK, 0 rows affected (0.00 sec)mysql> delete from product;Query OK, 9 rows affected (0.00 sec)mysql> select * from product;Empty set (0.00 sec)mysql> rollback;Query OK, 0 rows affected (0.00 sec)mysql> select * from product;+----+------------+---------+| id | pname      | price   |+----+------------+---------+|  1 | computer   | 999.999 ||  2 | phone      | 999.999 ||  3 | 笔记本         | 999.999 ||  4 | 智能手机          | 999.999 ||  5 | 洗衣机         | 999.999 ||  6 | 黑白电视机        | 999.999 ||  7 | 智能机器人          | 999.999 ||  8 | 彩色电视          | 999.999 ||  9 | 沙发          | 999.999 |+----+------------+---------+9 rows in set (0.00 sec)

Truncate操作演示:

mysql> start transaction;Query OK, 0 rows affected (0.00 sec)mysql> truncate table product;Query OK, 0 rows affected (0.00 sec)mysql> select * from product;Empty set (0.00 sec)mysql> rollback;Query OK, 0 rows affected (0.00 sec)mysql> select * from product;Empty set (0.00 sec)

注意：delete删除，uid不会重置！而使用truncate操作，uid会重置[因为它删除了表结构，然后再创建一张一模一样的表，所以再次插入数据的数据的时候从1开始。

查询操作

先创建表并添加数据

CREATE TABLE zhangwu (  id INT PRIMARY KEY AUTO_INCREMENT, -- 账务ID  zname VARCHAR(200), -- 账务名称  zmoney DOUBLE -- 金额);INSERT  INTO zhangwu(id,zname,zmoney) VALUES (1,‘吃饭支出‘,247);INSERT  INTO zhangwu(id,zname,zmoney) VALUES (2,‘工资收入‘,12345);INSERT  INTO zhangwu(id,zname,zmoney) VALUES (3,‘服装支出‘,1000);INSERT  INTO zhangwu(id,zname,zmoney) VALUES (4,‘吃饭支出‘,325);INSERT  INTO zhangwu(id,zname,zmoney) VALUES (5,‘股票收入‘,8000);INSERT  INTO zhangwu(id,zname,zmoney) VALUES (6,‘打麻将支出‘,8000);INSERT  INTO zhangwu(id,zname,zmoney) VALUES (7,NULL,5000);

语法：

select [distinct] *| 列名，列名 from 表名 [where条件]
/*   查询指定列的数据   格式:select 列名1,列名2 from 表名*/SELECT zname,zmoney FROM zhangwu;/*  查询所有列的数据  格式:select * from 表名*/SELECT * FROM zhangwu;/*   查询去掉重复记录   DISTINCT 关键字 跟随列名*/SELECT  DISTINCT zname FROM zhangwu/*  查询重新命名列  as 关键字*/SELECT zname AS ‘name‘ FROM zhangwu /*  查询数据中,直接进行数学计算  列对数字进行计算*/SELECT zname,zmoney+1000 AS‘sum‘ FROM zhangwu-- 查询所有的吃饭支出SELECT * FROM zhangwu WHERE zname=‘吃饭支出‘-- 查询金额大于1000SELECT * FROM zhangwu WHERE zmoney>1000-- 查询金额在2000到5000之间 SELECT * FROM zhangwu WHERE zmoney >= 2000 AND zmoney <= 5000-- 改造成between and 方式SELECT * FROM zhangwu WHERE zmoney BETWEEN 2000 AND 5000-- 查询金额是 1000,3500,5000 其中一个SELECT * FROM zhangwu WHERE zmoney = 1000 OR zmoney=3500 OR zmoney=5000-- 改造成in方式SELECT * FROM zhangwu WHERE zmoney  IN (1000,3500,5000)-- like 模糊查询 配合通配符-- 查询所有的支出SELECT * FROM zhangwu WHERE zname LIKE ‘%支出%‘-- 查询账务名字,五个字符的SELECT * FROM zhangwu WHERE zname LIKE‘_____‘-- 查询账务名,不为空的SELECT * FROM zhangwu WHERE zname IS NOT NULLSELECT * FROM zhangwu WHERE   NOT ( zname IS NULL)

排序

/*  查询,对结果集进行排序  升序,降序,对指定列排序  order by 列名 [desc][asc]  desc 降序  asc  升序排列,可以不写*/-- 查询账务表,价格进行升序SELECT * FROM zhangwu ORDER BY zmoney ASC-- 查询账务表,价格进行降序SELECT * FROM zhangwu ORDER BY zmoney DESC-- 查询账务表,查询所有的支出,对金额降序排列-- 先过滤条件 where 查询的结果再排序SELECT * FROM zhangwu WHERE zname LIKE‘%支出%‘ ORDER BY zmoney DESC

聚合函数

/*   使用聚合函数查询计算*/-- count 求和,对表中的数据的个数求和  count(列名)-- 查询统计账务表中,一共有多少条数据SELECT COUNT(*)AS‘count‘ FROM zhangwu-- sum求和,对一列中数据进行求和计算 sum(列名)-- 对账务表查询,对所有的金额求和计算SELECT SUM(zmoney) FROM zhangwu-- 求和,统计所有支出的总金额SELECT SUM(zname) FROM zhangwu WHERE zname LIKE‘%收入%‘INSERT INTO zhangwu (zname) VALUES (‘彩票收入‘)-- max 函数,对某列数据,获取最大值SELECT MAX(zmoney) FROM zhangwu-- avg 函数,计算一个列所有数据的平均数SELECT AVG(zmoney)FROM zhangwu

分组操作

/*    查询所有的数据    吃饭支出 共计多少    工资收入 共计多少    服装支出 共计多少    股票收入 共计多少    打麻将支出 共计多少钱        分组查询:  group by 被分组的列名    必须跟随聚合函数    select 查询的时候,被分组的列,要出现在select 选择列的后面*/  SELECT SUM(zmoney),zname FROM zhangwu GROUP BY zname  -- 对zname内容进行分组查询求和,但是只要支出SELECT SUM(zmoney)AS ‘getsum‘,zname FROM zhangwu WHERE zname LIKE‘%支出%‘GROUP BY znameORDER BY getsum DESC-- 对zname内容进行分组查询求和,但是只要支出, 显示金额大于5000-- 结果集是分组查询后,再次进行筛选,不能使用where, 分组后再次过滤,关键字 havingSELECT SUM(zmoney)AS ‘getsum‘,zname FROM zhangwu WHERE zname LIKE‘%支出%‘GROUP BY zname HAVING getsum>5000

查询总结

  • select 一般在后面的内容都是要查询的字段
  • from 要查询到表
  • where
  • group by
  • having 分组后带有条件只能使用having
  • order by 它必须放到最后面

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 更多请参考：《MySQL 必知必会》读书总结、《MySQL必知必会》读书笔记

Java基础学习笔记二十五 MySQL


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