mysql 基本操作

一、 数据库及对象

1、系统数据库

  • infomation_schema: 存放数据库对象信息,表信息、列信息,权限信息
  • performance_schema: 数据库服务器性能参数
  • mysql: 用户权限信息
  • sys : mysql5.7增加了sys 系统数据库,通过这个库可以快速的了解系统的元数据信息

2、操作

- 创建数据库 :  create database learn;
- 查询数据库 :  show databases;
- 选择数据库 :  use learn;
- 删除数据库 :  drop database learn;

二、 引擎与数据类型

1、引擎

查看引擎:show engines ; — show engines G

  • Transactions: 是否支持事务
  • XA: YES 分布式是否符合XA规范
  • Savepoints: 是否支持事务处理中的保存点

2、数据类型

- 整数类型 :
   - tinyint
   - smallint
   - mediumint
   - int,integer
   - bigint
- 浮点 : 
   - float
   - double
- 定点数类型 :
    - decimal->字符串存储
    - dec
- 日期 :
    - date 4字节
    - datetime 8字节
    - timestamp 4
    - time 3
    - year 1
- 字符串:
    - char 4
    - varchar 可变0~65535
    - tinytext -> text -> mediumtext -> longtext
    - tinyblob -> blob -> mediumblob -> longblob

三、 表操作

CREATE TABLE t_dept (
  dept_no   INT,
  dept_name VARCHAR(40),
  location  VARCHAR(80)
);
##描述表结构
desc t_dept;
## 查看创建语句
show create table t_dept;
##删除表
drop table t_dept;
##修改表名
alter table t_dept rename to t_deptartment;

##增加字段
alter table t_deptartment add dept_name_us VARCHAR(40);
##第一个位置增加字段
alter table t_deptartment add first_col VARCHAR(40) first;
## 某列后面添加字段
alter table t_deptartment add after_dept_name VARCHAR(80) after dept_name;
## 删除字段
alter table t_deptartment drop first_col;
##修改字段 数据类型
alter TABLE t_deptartment MODIFY after_dept_name VARCHAR(100);
## 修改字段名字 可以一同修改字段属性
ALTER TABLE t_deptartment CHANGE after_dept_name dept_name_after VARCHAR(10);

四、约束

##创建表的时候直接加入约束
CREATE TABLE t_dept (
  dept_no   INT(20) PRIMARY KEY NOT NULL, ##  非空约束
  type      VARCHAR(20) DEFAULT 'Co., Ltd', ##默认值
  dept_name VARCHAR(100) UNIQUE ##唯一值
);
desc t_dept  ;

##创建有名字的约束值
CREATE TABLE t_dept (
  dept_no   INT(20) AUTO_INCREMENT, ##自增
  type      VARCHAR(20),
  dept_name VARCHAR(100), 
  CONSTRAINT uk_dept_name UNIQUE (dept_name), ##唯一值
  CONSTRAINT pk_dept_no PRIMARY KEY (dept_no) ##一个字段主键
);

## 联合主键
CREATE TABLE t_dept1 (
  dept_no   INT(20) AUTO_INCREMENT, ##自增
  type      VARCHAR(20),
  dept_name VARCHAR(100), ##唯一值
  CONSTRAINT uk_dept_name1 UNIQUE (dept_name), ##唯一值
  CONSTRAINT pk_dept_no_name1 PRIMARY KEY (dept_no, dept_name) ##联合主键
);

#外键
CREATE TABLE t_employee (
  emp_no int(30) PRIMARY KEY,
  emp_name VARCHAR(20),
  dept_no  INT(20),
  CONSTRAINT fk_dept_no FOREIGN KEY (dept_no) REFERENCES t_dept(dept_no)
);

desc t_employee;

五、索引

1.索引类型

普通索引,唯一索引,全文索引,单列索引,多列索引,空间索引

适用: 经常被查询的字段,分组字段,主键或者外键。唯一完整性约束

不适用: 很少查询;拥有许多重复值的字段

2.语句
#普通索引
CREATE TABLE t_dept_2 (
  dept_no   INT,
  dept_name VARCHAR(20),
  loc       VARCHAR(40),
  INDEX index_dept_no(dept_no)
);

SHOW CREATE TABLE t_dept_2;
## 查看解析计划
EXPLAIN SELECT *
        FROM t_dept_2
        WHERE dept_no = 1;

## 单独创建索引
CREATE INDEX idx_dept_name
  ON t_dept_2 (dept_name);

ALTER TABLE t_dept_2
  ADD INDEX idx_loc(loc DESC);

## 唯一索引
CREATE TABLE t_dept_3 (
  dept_no INT UNIQUE,
  UNIQUE INDEX idx_dept_no(dept_no)
);
CREATE UNIQUE INDEX idx_dept_name
  ON t_dept_2 (dept_name);
ALTER TABLE t_dept_2
  ADD UNIQUE INDEX idx_loc(loc);

##全文索引
####默认不区分大小写,只能在数据类型char,varchar,text上创建
CREATE TABLE t_dept_4 (
  dept_no   INT,
  dept_name VARCHAR(20),
  FULLTEXT INDEX idx_dept_no (dept_name)
);
CREATE FULLTEXT INDEX idx_dept_name
  ON t_dept_2 (dept_name);
ALTER TABLE t_dept_2
  ADD FULLTEXT INDEX idx_loc(loc);

##多列索引
CREATE TABLE t_dept_5 (
  dept_no   INT,
  dept_name VARCHAR(20),
  INDEX idx_dept_no (dept_no, dept_name)
);
CREATE INDEX idx_dept_name
  ON t_dept_2 (dept_name);
ALTER TABLE t_dept_2
  ADD INDEX idx_loc(loc);

##删除索引
DROP INDEX idx_loc
ON t_dept_2;

六、视图

###创建视图
CREATE VIEW view_dept_no AS
  SELECT dept_no
  FROM t_dept;
  
select * from t_dept;
insert into t_dept (dept_no, dept_name) VALUES (1,'ccdata');

select * from view_dept_no ;

#查看view
show tables;
show table status from learn like 'view_dept_no';
use information_schema;
select * from views where table_name = 'view_dept_no' \G;

##删除view
drop view view_dept_no;

##修改视图
CREATE OR REPLACE VIEW view_dept_name
  AS
    SELECT dept_name
    FROM t_dept;
    
ALTER VIEW view_dept_name AS
  SELECT
    dept_no,
    dept_name
  FROM t_dept;
  
select * from   view_dept_name;
SELECT *
FROM t_dept;

##对视图的操作
insert into view_dept_name VALUES (2,'apple');
UPDATE view_dept_name set dept_name = 'Google' WHERE dept_no = 2;
delete from view_dept_name WHERE dept_no = 1;

七、触发器

## 语句
CREATE TRIGGER TRIGGER_NAME
  BEFORE | AFTER TRIGGER_EVENT
    ON TABLE_NAME FOR EACH ROW TRIGGER_STMT
    
## before|after 制定触发器触发的时间
## trigger_event 触发的事件(条件)
## for each row 每行改变都触发
## trigger_stmt 触发的语句

##准备
CREATE TABLE department (
  no       INT(12),
  name     VARCHAR(40),
  location VARCHAR(60)
);

CREATE TABLE diary (
  diary_no   INT(12) AUTO_INCREMENT PRIMARY KEY,
  table_name VARCHAR(50),
  diary_time DATETIME
);

## 创建触发器
CREATE TRIGGER trigger_diary_time
BEFORE INSERT ON department
FOR EACH ROW
  INSERT INTO diary (table_name, diary_time) VALUES ('department', now());

## 测试
INSERT INTO department VALUES (1, 'apple', 'Peking');
SELECT * FROM diary;

## 触发器中包含多个语句
CREATE TRIGGER trigger_diary_time
BEFORE INSERT ON department
FOR EACH ROW
  BEGIN
    INSERT INTO diary (table_name, diary_time) VALUES ('department', now());
    INSERT INTO diary (table_name, diary_time) VALUES ('department2', now());
  END;

## 创建多个语句时候,书上说;可能被当做结束符?(没碰到这种情况)
DELIMITER $$
CREATE TRIGGER trigger_diary_time
BEFORE INSERT ON department
FOR EACH ROW
  BEGIN
    INSERT INTO diary (table_name, diary_time) VALUES ('department', now());
    INSERT INTO diary (table_name, diary_time) VALUES ('department2', now());
  END;
$$
DELIMITER ;

## 查看
SHOW TRIGGERS;

USE information_schema;
SELECT * FROM TRIGGERS;

##删除
DROP TRIGGER trigger_diary_time;
    

八、数据操作

##插入数据
INSERT INTO t_dept_2 (dept_no, dept_name, loc) VALUES ('1', 'apple', 'Peking');
INSERT INTO t_dept_2 (dept_no, dept_name) VALUES ('2', 'Google');
INSERT INTO t_dept_2 VALUES ('3', 'Amazon', 'USA');

## 插入多个值
INSERT INTO t_dept_2 VALUES
  ('4', 'Tencent', 'Guangzhou'),
  ('5', '网易', '杭州'),
  ('6', '饿了吗', '北京');

## 别的表转移
INSERT INTO t_dept_2 (dept_name)
  SELECT dept_name
  FROM t_deptartment;

##### 更新
UPDATE T_DEPT_2 SET LOC= '美国' WHERE DEPT_NAME = 'GOOGLE';

##### 删除
delete from t_dept_2 WHERE dept_no = 6;

九、记录查询

## 去重复
SELECT DISTINCT
  DEPT_NAME,
  LOC
FROM T_DEPT_2;

## 数学运算
CREATE TABLE employee (
  no     INT(10),
  name   VARCHAR(20),
  salary DOUBLE(10, 2)
);

INSERT INTO employee VALUES
  (1, 'a', 1234),
  (2, 'b', 2500),
  (3, 'c', 3600),
  (4, 'd', 4500),
  (5, 'e', 7800);

SELECT
  name,
  salary + 100,
  salary - 200,
  salary * 1.2,
  salary / 1000,
  salary % 1000
FROM employee;
关系运算符
运算符描述

| 大于
< | 小于
= | 等于
!=(<>) | 不等于
= | 大于等于
<= | 小于等于

逻辑运算符
运算符描述
AND (&&)
OR (``)
XOR异或
NOT(!)
## 两侧都包括
select * from employee WHERE salary BETWEEN 2500 and 4500;
## 空值判断
select * from employee where salary is null;
## in 语句
select * from employee WHERE name in ('a','b');

## like 语句

select * from  employee WHERE salary like '4%';
select * from  employee WHERE salary like '4%00';
## 这样查不出来 why? (double 不太一样?)
select * from  employee WHERE salary like '4_00';
select * from  employee WHERE name like '_bc';

## 排序
select * from employee order by salary ;
select * from employee order by salary DESC;
SELECT * FROM EMPLOYEE ORDER BY SALARY DESC ,NO;

## 限制查询条数
select * from employee LIMIT 2;
## 指定初始位置 ,显示条猪
select * from employee LIMIT 2,4;

统计函数

select count(*) from employee;
select count(1) from employee;
select count(salary) from employee; -- 将忽略null值,不参与计数


## 平均值,null值既不计入和值也不计入 个数
select avg(salary) from employee;

select sum(salary) from employee;
select max(salary) from employee;
select min(salary) from employee;

## 分组
SELECT
  substr(salary, 1, 1),
  count(*)
FROM employee
GROUP BY substr(salary, 1, 1);

SELECT
  substr(salary, 1, 1),
  count(*)
FROM employee
GROUP BY substr(salary, 1, 1)
HAVING count(*) > 1;

十、多表查询


## 内连接
SELECT
  a.name,
  b.name,
  a.salary
FROM employee a
  JOIN employee b ON a.salary = b.salary AND a.name != b.name;

SELECT
  a.name,
  b.name,
  a.salary
FROM employee a, employee b
WHERE a.salary = b.salary
      AND a.name != b.name;

## 外链接
### 左外联结 left join on
### 右外联结 right join on
### 全外联结 full join on
select * from employee;
select * from t_dept_2 ;

select * from t_dept_2 a LEFT JOIN employee b on a.dept_no = b.dept_no;
select * from t_dept_2 a RIGHT JOIN employee b on a.dept_no = b.dept_no;
#####  mysql 不支持。。。 select * from t_dept_2 a FULL JOIN  

## 合并
#### union 合并重复记录
SELECT DEPT_NO FROM T_DEPT_2
UNION
SELECT NO FROM EMPLOYEE;

SELECT DEPT_NO FROM T_DEPT_2
UNION ALL
SELECT NO FROM EMPLOYEE;

## 子查询

SELECT *
FROM employee
WHERE (no, dept_no) IN (
  SELECT
    no,
    dept_no
  FROM employee
  WHERE salary > 4000);
  
##any
## 类似于 in
select * from employee WHERE salary = ANY (select salary from employee WHERE dept_no = 2);
## 大于最小值
select * from employee WHERE salary > ANY (select salary from employee WHERE dept_no = 2);
## 小于最大值
select * from employee WHERE salary < ANY (select salary from employee WHERE dept_no = 2);

##all
## 大于最大值
select * from employee WHERE salary > ALL (select salary from employee WHERE dept_no = 2);
## 小于最小值
select * from employee WHERE salary < ALL (select salary from employee WHERE dept_no = 2);


## exists
SELECT *
FROM employee a
WHERE exists(
    SELECT *
    FROM t_dept_2 b
    WHERE a.dept_no = b.dept_no
);

##  not exists
SELECT *
FROM employee a
WHERE NOT exists(
    SELECT *
    FROM t_dept_2 b
    WHERE a.dept_no = b.dept_no
);

十一、运算符

## 算数运算符
SELECT
  6 + 4,
  6 - 4,
  6 / 2,
  6 DIV 2,
  6 % 4,
  6 MOD 4;
  
 ## 结果: 10,2,3.0000,3,2,2
 ## Why?
 ###  The MySQL DIV function is used for integer division where n is divided by m and an integer value is returned.


    原文作者:kyle
    原文地址: https://segmentfault.com/a/1190000012149871
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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