Mysql数据库总结

三、Sql语句

(1)Sql语句简介

• SQL(Structured Query Language):结构化查询语言
• SQL是在关系数据库上执行数据操作、检索及维护所使用的标准语言，可以用来查询数据，操纵数据，定义数据，控制数据。

SQL可以分为：

• 数据定义语言(DDL)：Data Definition Language
• 数据操纵语言(DML)：Data Manipulation Language
• 事务控制语言(TCL)：Transaction Control Language
• 数据查询语言(DQL)：Data Query Language
• 数据控制语言(DCL)：Data Control Language

(2)数据定义语言DDLcreate,alter,drop

--数据定义语言DDL(create,alter,drop)

– 一、数据库相关的DDL

– 1.创建数据库
CREATE DATABASE mybase;
– 2.创建数据库并指定字符集
CREATE DATABASE mybase1 CHARACTER SET UTF8;
– 3.查看所有数据库
SHOW DATABASES;
– 4.查看当前使用的数据库
SELECT DATABASE();
– 5.修改数据库
ALTER DATABASE mybase CHARACTER SET UTF8;
– 6.删除数据库
DROP DATABASE mybase1;
– 切换数据库
USE mybase;

–二、表相关DDL

– 1.创建表
create table exam(
id INT(11) PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(20),
English INT,
Chinese INT,
Math int
);
– 2.查看数据库中所有表
show TABLES;
– 3.查看表结构
desc exam;

– 4.表的删除
drop table exam;

– 5.表的修改(基于exam表)

– 5.1添加列
ALTER TABLE exam ADD History INT NOT NULL;
– 5.2修改列的类型、长度、约束
ALTER TABLE exam MODIFY History DOUBLE(7,2);
– 5.3修改表的列名
ALTER TABLE exam CHANGE History Physics INT NOT NULL;
– 5.4修改表名
RENAME TABLE exam TO score;
– 5.5修改表的字符集
ALTER TABLE score CHARACTER SET GBK;
– 5.6删除列
ALTER TABLE score DROP Physics;
– 5.7

ALTER TABLE

– 三、练习:创建emp表

CREATE TABLE emp(
empno INT PRIMARY KEY AUTO_INCREMENT,
ename VARCHAR(20),
job VARCHAR(20),
mgr int,
hiredate DATE,
sal DOUBLE(7,2),
commit double(5,2),
deptno INT NOT NULL – 非空约束
);

表exam:

表emp:

(3)数据操纵语言DMLupdate,insert,delete

-- 数据操纵语言DML(update,insert,delete)

– 1.插入部分列
INSERT INTO score(id,NAME,English,Chinese,Math) VALUE(1,‘Hudie’,90,90,90);
INSERT INTO score(id,NAME,English,Chinese) VALUE(NULL,‘diedie’,91,91);
– 2.插入所有列
INSERT INTO score VALUES(3,‘Shu’,80,80,80);
– 3.修改记录
UPDATE score set Chinese=99; –全表修改
UPDATE score SET Math=100 WHERE id=‘1’;
– 4.删除记录
DELETE FROM score WHERE id=‘2’;
DELETE FROM score;

– delete与truncate的区别 √
–TRUNCATE TABLE 删除表的记录:将整个表删除掉,重新创建一个新的表,属于DDL.
–DELETE FROM 删除表的记录:一条一条进行删除,DELETE.
INSERT INTO score VALUES(3,‘Shu’,80,80,80);
DELETE FROM score;
INSERT INTO score VALUES(NULL,‘Libai’,10,10,10); –不会清空AUTO_INCREMENT值
TRUNCATE TABLE score;
INSERT INTO score VALUES(NULL,‘Libai’,10,10,10); –清空AUTO_INCREMENT的值

– 事务管理:只能作用在DML语句上,如果在一个事务中使用delete删除所有记录,可以找回.
– 使用delete删除后可以用COMMIT和ROLLBACK找回数据,使用truncate后就找不回来了.

– delete、truncate、drop的区别 √
delete、truncate、只是删除表的记录,而drop会直接删除表.

(4)数据控制语言DCLgrant,revoke

-- 数据控制语言DCL(grant,revoke)
-- 主要为用户授予和撤销权限

– 1.创建用户:CREATE USER 用户名@ip IDENTIFIED BY 密码;
create user Fox@localhost identified by ‘123456’;

– 2.给用户授权:grank 权限1,权限2,…,权限n ON 数据库名.* TO 用户名@IP;
grant select,drop on mysql.* to Fox@localhost;

– 3.撤销权限:REVOKE 权限1,权限2,…,权限n ON 数据库名.* FROM 用户名@IP;
revoke select on mysql.* from Fox@localhost;

– 4.查看用户的权限:SHOW GRANTS FOR 用户名@IPl
show grants for Fox@localhost;
– 5.删除用户: DROP USER 用户名@IP;
drop user Fox@localhost;
– 6.登录:mysql -u 用户名-p 密码;
mysql -u root -p
– 7.退出登录: exit;
exit;

(5)数据查询语言DQLselect

exam表：

-- 数据查询语言DQL(select)
create table exam(
	id INT(11) PRIMARY KEY AUTO_INCREMENT,
	name VARCHAR(20),
	English INT,
	Chinese INT,
	Math int
);
INSERT INTO exam VALUES(NULL,'小花',99,99,99);
INSERT INTO exam VALUES(NULL,'小蓝',89,89,89);

– 1.全表查询: SELECT * FROM 表;
SELECT FROM exam;
– 2.查询部分字段: SELECT 字段,字段,字段… FROM 表;
SELECT NAME,English,Math FROM exam;
– 3.过滤重复字段行: SELECT [DISTINCT] |列名 FROM 表;
SELECT DISTINCT Math FROM exam;
SELECT DISTINCT name,Math FROM exam;
– 4.查询字段起别名: SELECT 字段 AS 新字段名,字段 新字段名 FROM 表;
SELECT NAME,English AS English_score FROM exam;
– 5.查询指定字段
SELECT NAME,English,Chinese FROM exam WHERE NAME=‘李白’;
– 6.使用表达式+、-、、/
SELECT id,NAME,English-20 AS _English FROM exam;
SELECT NAME,English+Math+Chinese FROM exam;
– 7.模糊查询
SELECT FROM exam WHERE NAME LIKE ‘小_’;
SELECT FROM exam WHERE NAME LIKE ‘%%’;
– 8.使用and,or
SELECT FROM exam WHERE English > 90 AND Chinese >90;
SELECT FROM exam WHERE English < 90 or Math >99;
– 9.使用in,not in
SELECT FROM exam WHERE id=2 OR id=3 OR id=4;
SELECT FROM exam where id IN(2,3,4);
SELECT FROM exam where id not IN(2,3,4);
– 10.使用between…and []
SELECT FROM exam WHERE English BETWEEN 90 AND 100;
– 11. is null,is not null
INSERT INTO exam(id,NAME) VALUES(NULL,NULL);
SELECT FROM exam WHERE NAME IS NULL;
SELECT FROM exam WHERE NAME IS not NULL;
– 11.排序查询
SELECT FROM exam ORDER BY Chinese ASC;
SELECT FROM exam ORDER BY Chinese DESC;
SELECT FROM exam ORDER BY English DESC,Chinese DESC;– 如果英语成绩相同,按照汉语成绩降序排列
SELECT * FROM exam WHERE NAME LIKE ‘小%’ ORDER BY English ASC;
– 12.聚合函数
SELECT SUM(English+Math+Chinese) FROM exam;
SELECT COUNT(id) FROM exam WHERE NAME IS NOT NULL;
SELECT MAX(English) FROM exam;
SELECT MIN(English) FROM exam;
SELECT AVG(English) FROM exam ;

(6)分组查询与分页查询group by，limit

-- 一、分组查询

CREATE TABLE emp(
empno INT PRIMARY KEY AUTO_INCREMENT,
ename VARCHAR(20),
job VARCHAR(20),
mgr int,
hiredate DATE,
sal DOUBLE(7,2),
commit double(5,2),
deptno INT NOT NULL
);

INSERT INTO emp VALUES
(1002,‘白展堂’,‘clerk’,1001,‘1983-05-09’,7000.00,200.00,10),
(1003,‘李大嘴’,‘clerk’,1002,‘1980-07-08’,8000.00,100.00,10),
(1004,‘吕秀才’,‘clerk’,1002,‘1985-11-12’,4000.00,null,10),
(1005,‘郭芙蓉’,‘clerk’,1002,‘1985-03-04’,4000.00,null,10),
(2001,‘胡一菲’,‘leader’,null,‘1994-03-04’,15000.00,NULL,20),
(2002,‘陈美嘉’,‘manger’,2001,‘1993-05-24’,10000.00,300.00,20),
(2003,‘吕子乔’,‘clerk’,2002,‘1995-05-19’,7300.00,100.00,20),
(2004,‘张伟’,‘clerk’,2002,‘1994-10-12’,8000.00,500.00,20),
(2005,‘曾小贤’,‘clerk’,2002,‘1993-05-10’,9000.00,700.00,20),
(3001,‘刘梅’,‘leader’,null,‘1968-08-08’,13000.00,NULL,30),
(3002,‘夏冬梅’,‘manger’,3001,‘1968-09-21’,10000.00,600.00,30),
(3003,‘夏雪’,‘clerk’,3002,‘1989-09-21’,8000.00,300.00,30),
(3004,‘张一山’,‘clerk’,3002,‘1991-06-16’,88000.00,200.00,30);

– 1.查询每个部门的平均工资
SELECT deptno,AVG(sal) FROM emp GROUP BY deptno;
– 2.查询每个职位的最高工资和最低工资
SELECT job,MAX(sal),MIN(sal) FROM emp GROUP BY job;
– 3.查询每个部门每种职位的最高工资
SELECT deptno,job,MAX(sal) FROM emp GROUP BY deptno,job;
– 4.查询每个部门的最高薪水,只有最高薪水大于15000的记录才被输出显示
SELECT deptno,MAX(sal)AS max_sal FROM emp GROUP BY deptno HAVING max_sal>=15000;
– 5.查询每个部门的平均工资
SELECT deptno,AVG(sal) FROM emp GROUP BY deptno HAVING AVG(sal)>9000;
– 6.Havaing子句与where子句的区别
(1)where是用来过滤记录的,HAVING是用来过滤分组的
(2)过滤的时机不相同,先过滤Where后过滤Having.
(3)WHERE是在查询表时逐行过滤以选取满足条件的记录
(4)having是在数据查询后并且分完组后对分组进行过滤的
(5)HAVING必须跟在group BY
(6)查询语句执行顺序:5select 1from 2where 3group by 4having 6order by

– 二、分页查询
– 1.从第几页开始多少页(下标从0开始)
SELECT FROM emp LIMIT 0,3;
– 2.每页几条第几页==需要查看第几页-1)乘以第二个参数
SELECT FROM emp LIMIT 10,5;– 每页五条第三页(3-1)5
SELECT FROM emp LIMIT 2,2; –每页2条第2页(2-1)2
– 3.查看工资最高的前十个职员信息
SELECT FROM emp ORDER BY sal DESC LIMIT 0,10;

四、完整性约束(单表)

主键约束：primary key (默认就是唯一非空的)
外键约束:   用于在两个表之间建立关系，需要指定引用主表的哪一列。

• 如果表A的主键是表B中的字段,则该字段称为表B的外键,表A(主表),表B(从表).
• 外键是用来实现参照完整性的，主表更新时从表也更新,主表删除时如果从表有匹配的项,删除失败

唯一约束：unique
非空约束：not null

CREATE TABLE emp(
	empno INT PRIMARY KEY AUTO_INCREMENT,--主键约束
	ename VARCHAR(20),
	job VARCHAR(20),
	mgr int,
	hiredate DATE,
	sal DOUBLE(7,2),
	commit double(5,2),
	deptno INT NOT NULL	-- 非空约束
);
-- √ 添加 唯一约束和非空约束
ALTER TABLE exam MODIFY NAME VARCHAR(21) UNIQUE NOT NULL;

– 创建主表
CREATE TABLE dept(
deptno INT PRIMARY KEY,
dname VARCHAR(20),
loc VARCHAR(20)
);
INSERT INTO dept VALUES
(10,‘餐饮部’,‘上海’),
(20,‘销售部’,‘浙江’),
(30,‘财务部’,‘北京’),
(40,‘技术部’,‘深圳’);

为从表emp加外键

ALTER TABLE emp ADD FOREIGN KEY (deptno) REFERENCES dept(deptno);

五、多表查询

多张数据表或视图的查询叫做连接查询

– 1.笛卡尔积:
SELECT
FROM emp,dept;
– 2.等值链接(SELECT * FROM A,B WHERE A.主键=B.外键;)
SELECT
FROM emp,dept WHERE dept.deptno = emp.deptno;
– 3.内连接(SELECT * FROM A INNER JOIN B ON A.主键=B.外键;)
SELECT
FROM emp INNER JOIN dept ON dept.deptno = emp.deptno;
– 4.外连接:
– 4.1左外连接:(SELECT * FROM A LEFT OUTER JOIN B ON 条件;)
SELECT
FROM emp LEFT OUTER JOIN dept ON dept.deptno=emp.deptno;
– 4.2右外连接:(SELECT * FROM A right OUTER JOIN B ON 条件;)
SELECT
FROM emp RIGHT OUTER JOIN dept ON dept.deptno=emp.deptno;
– 5.子查询:
– 5.1单行单列,工作地点在上海的员工
SELECT
FROM emp WHERE deptno=(SELECT deptno FROM dept WHERE loc =‘上海’);
– 5.2多行单列,工作地点不在上海的员工
SELECT
FROM emp WHERE deptno in(SELECT deptno FROM dept WHERE loc <>‘上海’);
– 6.自连接
SELECT e1.,e2.* FROM emp e1 inner join emp e2 ON e1.mgr =e2.empno
WHERE e1.ename =‘吕子乔’

多表查询练习↓
– 1.查看每个员工的名字以及其所在部门的名字
SELECT emp.ename,dept.dname,dept.loc
FROM emp,dept
WHERE emp.deptno = dept.deptno;
– 2.查看工作地点在北京的员工有哪些
SELECT
FROM emp INNER JOIN dept ON emp.deptno = dept.deptno
WHERE dept.loc =‘北京’;
– 3.查看每个城市员工的平均工资
SELECT dept.loc,ifnull(avg(sal),0)
FROM emp right join dept
on emp.deptno =dept.deptno
GROUP BY dept.loc;
– 4.查看工作地点在上海的员工有哪些
SELECT emp.,dept.dname,dept.loc
FROM emp LEFT OUTER JOIN dept ON emp.deptno=dept.deptno
WHERE dept.loc=‘上海’;
– 5.查找和曾小贤同职位的员工
SELECT
FROM emp
WHERE job=(SELECT job FROM emp WHERE ename=‘曾小贤’);
– 6.查找薪水比整个机构平均水平高的员工
SELECT
FROM emp
WHERE sal>(SELECT AVG(sal) FROM emp);
– 7.查询出部门中有clerk但职位不是clerk的员工的信息
SELECT *
FROM emp
WHERE deptno IN(SELECT DISTINCT deptno FROM emp WHERE job=‘clerk’) AND job!=‘clerk’;
– 8.查看每个城市员工的平均工资’
SELECT dept.loc,AVG(sal)
FROM emp INNER JOIN dept ON emp.deptno=dept.deptno GROUP BY dept.loc;
– 9.查询出最低薪水高于部门20的最低薪水的部门信息
SELECT deptno,MIN(sal) AS MIN_sal
FROM emp
GROUP BY deptno
HAVING min_sal>(SELECT MIN(sal) FROM emp WHERE deptno=20);
– 10.列出所有员工的姓名及其直接上级的姓名
SELECT e1.ename,e2.ename
FROM emp e1
LEFT JOIN emp e2 ON e1.mgr = e2.empno;

六、MySQL数据库练习题

练习题

转载：https://blog.csdn.net/qq_15719613/article/details/106860778