Mysql数据库基础知识点（函数，视图）/四

mysql常见函数总结

数值函数
绝对值
select abs(-3) from dual;
向下取整
select floor(3.456) from dual;
向上取整
select ceil(3.1) from dual;
拼接字符串
select concat('hello','world') from dual;
查看数据库
select database() from dual;
查看数据库版本
select version() from dual;
查看数据库密码
select PASSWORD('root') from dual;

视图

视图：视图就是一条SELECT语句执行后返回的结果集,

视图作用：简化用户的操作，对机密数据提供保护作用

创建表

CREATE TABLE t_employee(
        ID INT  PRIMARY KEY  AUTO_INCREMENT,
        NAME CHAR(30) NOT NULL,
        GENDER  CHAR(2) NOT NULL,
        AGE INT NOT NULL,
        DEPARTMENT CHAR(10) NOT NULL,
        SALARY  INT NOT NULL,
        HOME CHAR(30),
        MARRY CHAR(2) NOT NULL DEFAULT  '否',       
        HOBBY CHAR(30)
 );
create TABLE t_employee_detail(
ID INT PRIMARY KEY,
POS CHAR(10) NOT NULL,
EXPERENCE CHAR(10) NOT NULL,
CONSTRAINT `FK_ID` FOREIGN KEY(ID) REFERENCES t_employee(ID)
);

INSERT INTO t_employee(NAME, GENDER, AGE,DEPARTMENT, SALARY, HOME, MARRY, HOBBY) VALUES('张飞','女',21,'人事部','9000','北京','否','网球');

INSERT INTO t_employee(NAME, GENDER, AGE,DEPARTMENT, SALARY, HOME, MARRY, HOBBY) VALUES('刘备','男',22,'研发部','8000','上海','否','音乐');

INSERT INTO t_employee(NAME, GENDER, AGE,DEPARTMENT, SALARY, HOME, MARRY, HOBBY) VALUES('关羽','女',23,'研发部','9000','重庆','否','无');

INSERT INTO t_employee(NAME, GENDER, AGE,DEPARTMENT, SALARY, HOME, MARRY, HOBBY) VALUES('马超','女',24,'研发部','9000','四川','是','足球');

INSERT INTO t_employee(NAME, GENDER, AGE,DEPARTMENT, SALARY, HOME, MARRY, HOBBY) VALUES('赵云','男',25,'销售部','6000','福建','否','游戏');

INSERT INTO t_employee(NAME, GENDER, AGE,DEPARTMENT, SALARY, HOME, MARRY, HOBBY) VALUES('诸葛亮','女',26,'销售部','5000','山西','否','篮球');

INSERT INTO t_employee_detail(ID,POS,EXPERENCE) VALUES(1,'人事管理','工作二年');

INSERT INTO t_employee_detail(ID,POS,EXPERENCE) VALUES(2,'人事招聘','工作二年');

INSERT INTO t_employee_detail(ID,POS,EXPERENCE) VALUES(3,'初级工程师','工作一年');

INSERT INTO t_employee_detail(ID,POS,EXPERENCE) VALUES(4,'中级工程师','工作二年');

INSERT INTO t_employee_detail(ID,POS,EXPERENCE) VALUES(5,'高级工程师','工作三年');

INSERT INTO t_employee_detail(ID,POS,EXPERENCE) VALUES(6,'销售代表','工作二年');

-- 练习1: 创建一个员工基本信息的视图。
select * from t_employee;
select name,gender,age,home,marry,hobby from t_employee;

创建视图
create view v_t_employee as select age,home,marry,hobby from t_employee;
select * from v_t_employee;

-- 练习2：将员工所有的信息做成一个视图。

select * from t_employee as t1 LEFT JOIN t_employee_detail as t2 on t1.id=t2.id;

创建视图
create view v_emp_detail as select t1.*,t2.POS,t2.EXPERENCE from t_employee as t1 LEFT JOIN t_employee_detail as t2 on t1.id=t2.id;
select * from v_emp_detail;

修改表视图也会发生变化