第七周 Java语法总结之数据库大全_DDL_DML_DQL_约束_备份与还原_表的关系_三大范式_多表查询(内连接_外连接_子查询)_musql事务_隔离级别
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文章目录
数据库
DDL语句:数据库定义语句
1.库的增删查改
1.查询当前mysql下所有的数据库
mysql8.0 自带的 跟5.5自带的不一样
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema | mysql默认的一些配置
| mysql | mysql库里面包含user表用户表 (权限用户)
| performance_schema | mysql性能相关的库
| sakila | 提供其他三个库 sakila sys world 提供了一些例库 练习sql语句
| sys |
| world |
| zy | 自定义的库(开发者自定义)
+--------------------+
7 rows in set (0.00 sec)
2.创建数据库
create database 库名 ;
方式1
mysql> create database mydb_01;
Query OK, 1 row affected (0.02 sec)
create database if not exists 库名;
方式2
mysql> create database if not exists mydb_02;
Query OK, 1 row affected (0.02 sec)
3.查看创建数据库的默认的字符集(了解)
show create database 库名;
mysql> show create database mydb_01;
+----------+-----------------------------------------------------------------------------------------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------------------------------------------------------------------------------------+
| mydb_01 | CREATE DATABASE `mydb_01` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+-----------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
4.修改数据库的字符集(了解)
alter database 库名 (default)可以省略 character set=字符集;
mysql> alter database mydb_01 default character set gbk ;
Query OK, 1 row affected (0.01 sec)
mysql> show create database mydb_01;
+----------+----------------------------------------------------------------------------------------------------+
| Database | Create Database |
+----------+----------------------------------------------------------------------------------------------------+
| mydb_01 | CREATE DATABASE `mydb_01` /*!40100 DEFAULT CHARACTER SET gbk */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+----------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql>
5.删除库
drop database 库名;
drop database if exists 库名;
mysql> drop database mydb_02;
Query OK, 0 rows affected (0.02 sec)
mysql> drop database if exists mydb_03;
Query OK, 0 rows affected (0.01 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mydb_01 |
| mysql |
| performance_schema |
| sakila |
| sys |
| world |
| zy |
+--------------------+
6.模糊查询mysql服务中所有的带character字符集的全局变量
show variables like '%character%' ;
mysql> show variables like '%character%' ;
+--------------------------+---------------------------------------------------------+
| Variable_name | Value |
+--------------------------+---------------------------------------------------------+
| character_set_client | gbk |
| character_set_connection | gbk |
| character_set_database | utf8mb4 |
| character_set_filesystem | binary |
| character_set_results | gbk |
| character_set_server | utf8mb4 |
| character_set_system | utf8mb3 |
| character_sets_dir | C:\\Program Files\\MySQL\\MySQL Server 8.0\\share\\charsets\\ |
+--------------------------+---------------------------------------------------------+
8 rows in set, 1 warning (0.01 sec)
如果出现中文乱码:
character_set_client 客户端 utf8
character_set_results 结果集 utf8
改动字符集:临时解决中文乱码
mysql> set character_set_client=utf8;
Query OK, 0 rows affected, 1 warning (0.01 sec)
mysql> set character_set_results=utf8;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> show variables like '%character%' ;
+--------------------------+---------------------------------------------------------+
| Variable_name | Value |
+--------------------------+---------------------------------------------------------+
| character_set_client | utf8mb3 |
| character_set_connection | gbk |
| character_set_database | ut
f8mb4 |
| character_set_filesystem | binary |
| character_set_results | utf8mb3 |
| character_set_server | utf8mb4 |
| character_set_system | utf8mb3 |
| character_sets_dir | C:\\Program Files\\MySQL\\MySQL Server 8.0\\share\\charsets\\ |
+--------------------------+---------------------------------------------------------+
8 rows in set, 1 warning (0.00 sec)
2.表的增删改查
1.创建表
create table 表明(
列名1 字段类型1,
列名2 字段类型2,
...
列名n 字段类型n
) ;
数据库常用的字段类型
int------>默认int(11) 取的是当前实际长度 (推荐)
id int,---编号 1
int(长度):指定长度
id int(3) 1---->001
varchar(字符长度):字符串类型数据 '' "" 不写 引号 ,习惯去使用''或者双引号
double(值1,值2):小数类型
举例
double(3,2) ----小数类型,3位数,小数点后保留2位
123.56
日期类型
date 仅仅表示日期,不表示时分秒
"2021-8-12"
datatime 不仅表示日期具体的时间
"2021-8-12 17:31:00"
timestap:时间戳
给表中插入数据, 显示当前插入/修改/删除/查询数据那一刻时间 (具体到秒"2021-8-12 18:00:01")
注意事项:就是给那一个库中创建表 使用哪个库(选择数据库名)
use 库名;
mysql> use mydb_01;
Database changed
mysql>
mysql> create table student(
-> id int,
-> name varchar(20),
-> gender varchar(10),
-> address varchar(50),
-> age int
-> )
-> ;
Query OK, 0 rows affected (0.05 sec)
2.查询当前数据库中有哪些表
show tables ;
mysql> show tables;
+-------------------+
| Tables_in_mydb_01 |
+-------------------+
| student |
+-------------------+
1 row in set (0.01 sec)
3.查询当前表的结构
desc 表名 ;
mysql> desc student;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| gender | varchar(10) | YES | | NULL | |
| address | varchar(50) | YES | | NULL | |
| age | int | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.01 sec)
修改表
4.给student表添加一列
alter table 表名 add 字段名称 字段类型;
mysql> alter table student add email varchar(50) ;
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| gender | varchar(10) | YES | | NULL | |
| address | varchar(50) | YES | | NULL | |
| age | int | YES | | NULL | |
| email | varchar(50) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.01 sec)
5.修改表中的字段类型
alter table 表名 modify 字段名称 更改后的字段类型;
mysql> alter table student modify address varchar(30) ;
Query OK, 0 rows affected (0.07 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| gender | varchar(10) | YES | | NULL | |
| address | varchar(30) | YES | | NULL | |
| age | int | YES | | NULL | |
| email | varchar(50) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)
6.修改表中的字段名称
alter table 表名 change 旧列名 新列名 字段类型;
mysql> alter table student change gender sex varchar(10) ;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| sex | varchar(10) | YES | | NULL | |
| address | varchar(30) | YES | | NULL | |
| age | int | YES | | NULL | |
| email | varchar(50) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.01 sec)
7.删除某一列字段
alter table 表名 drop 字段名称;
mysql> alter table student drop email;
Query OK, 0 rows affected (0.06 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| sex | varchar(10) | YES | | NULL | |
| address | varchar(30) | YES | | NULL | |
| age | int | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.01 sec)
8.修改表的表名
alter table 旧表名 renameto 新表名;
mysql> alter table student rename to stu;
Query OK, 0 rows affected (0.03 sec)
mysql> show tables;
+-------------------+
| Tables_in_mydb_01 |
+-------------------+
| stu |
| teacher |
+-------------------+
2 rows in set (0.01 sec)
9.复制一张表结构和以前表的结果一样
create table 新表名 like 旧表名;
mysql> create table teacher like student; //字段复制
Query OK, 0 rows affected (0.03 sec)
mysql> show tables;
+-------------------+
| Tables_in_mydb_01 |
+-------------------+
| student |
| teacher |
+-------------------+
2 rows in set (0.01 sec)
10.删除表
drop tabble 表名;
drop table if exists 表名;
mysql> drop table if exists teacher;
Query OK, 0 rows affected (0.03 sec)
mysql> show tables;
+-------------------+
| Tables_in_mydb_01 |
+-------------------+
| stu |
+-------------------+
1 row in set (0.00 sec)
DML语句:操作表的记录
11.插入语句
1）**insert into 表名 values(值1,值2,值3…) ;**插入全表数据 :那么每一个参数值必须和字段类型匹配! (不会报错,警告)
mysql> insert into stu values(1,'高圆圆','女','西安市',30) ;
Query OK, 1 row affected (0.01 sec)
插入全表:一次性插入多条数据
2）insert into 表名 values(值1,值2…),(值1,值2…),(值1,值2…) ;
INSERT INTO
stu
VALUES
(3,'文章','男','西安市',35),
(4,'马伊琍','女','上海市',42),
(5,'德玛西亚','男','艾欧尼亚',25) ;
插入部分字段
3） insert into 表名(部分字段1,字段2…) values(值1,值2…)
INSERT INTO
stu(NAME,sex,address) VALUES('王宝强','男','咸阳市') ;
-- 注意:插入部分字段,必须字段数量和插入值的数量必须匹配
-- 不管插入部分字段还全部字段,那么必须要和当前类型一致
12.最基本的查询:查全表数据
select * from 表名;
mysql> insert into stu values(1,'高圆圆','女','西安市',30) ;
Query OK, 1 row affected (0.01 sec)
mysql> select * from stu ;
+------+--------+------+---------+------+
| id | name | sex | address | age |
+------+--------+------+---------+------+
| 1 | 高圆圆 | 女 | 西安市 | 30 |
+------+--------+------+---------+------+
1 row in set (0.01 sec)
如果中文乱码
改动下面的字符集编码即可
mysql> show variables like '%character%' ;
+--------------------------+---------------------------------------------------------+
| Variable_name | Value |
+以上是关于第七周 Java语法总结之数据库大全_DDL_DML_DQL_约束_备份与还原_表的关系_三大范式_多表查询(内连接_外连接_子查询)_musql事务_隔离级别的主要内容，如果未能解决你的问题，请参考以下文章