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Java基础学习笔记二十五 MySQL
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】
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
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