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Database:
a warehouse for storing data -
Relational database Mysql oracle SqlServer BD2 Non-relational database nosql
redis mongodb -
Database programming language
Database definition language DDL
Database operation language DML -
3 build 4 sentences: build database, build table, build constraint CRUD (addition, deletion, modification, check),
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-Requirements for library names
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Must start with a letter
基础语句 ##建库 create DATABASE xyi; ##使用库 USE xyi ##删库 DROP xyi； ##建表 CREATE TABLE user{ id INT, name VARCHAR(64） } ##设置字符集 SET character_set_client=utf-8; ##删表 DROP TABLE user； ##改表名 AlTER TABLE user RENAME uuu; 或者 RENAME TABLE uuuu TO user； ## 查看表的结构 DESC user； ##约束 ##主键约束 PRIMARY KEY ##自增约束 AUTO_INCREMENT ##非空约束 NOT NULL ##唯一 UNIQUE ##默认值约束 DEFAULT 值 ##外键 FOREIGN KEY
Completely establish the library, add, delete, modify and check it
##建表
CREATE TABLE stu{
id INT PRIMARY KEY AUTO_INCREMENT, ##AUTO_INCREMENT表示会自动生成
NAME VARCHAR(64) DEFAULT 'jack', ##DEFAULT表示后面是该默认值
age INT DEFAULT 18,
address VARCHAR(64)
}
##添加数据
INSERT INTO stu(id,NAME,age,address) VALUES(NULL,'张三',20,'武汉');
##添加多条数据
INSERT INTO stu VALUES
(NULL,"熊一",18,'武汉')
(NULL,"熊孩子",18,'湖北')
##只想添加某些数据
INSERT INTO stu(NAME) VALUES(‘张三’);
##删除数据
DELETE FROM stu WHERE id=2;
##修改数据
UPDATE stu SET NAME=‘路飞’,age='20',address='东海' WHERE id=7;
##查询数据
SELECT * FROM stu;
##查询条件
SELECT * FROM stu WHERE address='武汉'
## 查询中的 逻辑与AND 逻辑或or
SELECT * FROM stu WHERE address='武汉' AND age=20
SELECT * FROM stu WHERE age =18 or age=22
## 查询中的 逻辑或in
SELECT * FROM stu WHERE age IN(18,22,25);
##统计 COUNT
SELECT COUNT(*) FROM stu;
##分组（用年龄分组）
SELECT * FROM stu GROUP BY age
SELECT age,COUNT(*) FROM stu GROUP BY age
##排序
SELECT * FROM stu ORDER BY age ASC; ##升序
SELECT * FROM stu ORDER BY age DEDC ##降序
##分页
SELECT * FROM stu LIMIT 3; ##获取前面的三条数据显示出来
SELECT * FROM stu LIMIT 0,3 ; ##参数 起始索引，展示的条数
SELECT * FROM stu LIMIT 3,3