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 MySQL PS: 

## , , , ?

- **** : (DataBase  DB)
- **** : (Database Management System  DBMS)
- **** : (Data Base System DBS)(DBA)
- **** : (Database Administrator,  DBA)

## , , , , , , 

- ****  tuple 
- **** 
- ****  {}{}
- **** :  
- **** : 
- ****   . 
- **** 

##  ER 

 ER 

**ER **  Entity Relationship Diagram

ER  3 

- ****  ER 
- ****  ER 
- **** 

 ER M: N1  11:11 1: N

![E-R](https://img-blog.csdnimg.cn/img_convert/c745c87f6eda9a439e0eea52012c7f4a.png)

## ?

 3 

- 1NF()
- 2NF()1NF 
- 3NF()3NF  2NF  

### 1NF()

**1NF ** 

### 2NF()

2NF  1NF 

![](https://img-blog.csdnimg.cn/img_convert/bd1d31be3779342427fc9e462bf7f05c.png)



- **functional dependency** X  Y  Y  X X  Y
- **partial functional dependency**  XY X  X0 X0Y Y  X  R  R ->->->
- **(Full functional dependency)**  R R ->->()->()
- ****   R(U) XYZ  U  X  YY  Z X  YY  XXYZ= Z (transitive functional dependency)  X Y  Z  R( , , )    

### 3NF()

3NF  2NF   3NF **** R( , , )     3NF 

## ?

- **()** 
- **()** 

## 



> 
>
> :  student_id  student_id  student_id student_id ;  ; 



1. **** a.  DELETE  UPDATE , ; b. 
2. **** 
3. **** 
4. ......



1. 
2. 
3. ......



## ?

 SQL  SQL  SQL 



 Java 

![Java: ](https://img-blog.csdnimg.cn/img_convert/0fa082bc4d4f919065767476a41b2156.png)

## dropdelete  truncate 

### 

- `drop`(): `drop table ` 
- `truncate` () : `truncate table `  id  1 
- `delete` : `delete from  where =` `where` `truncate table `

`truncate`  where`` `delete` `drop`  **`truncate`  `delete` () `drop`  `drop` **

### 

`truncate`  `drop`  DDL() rollback segment  trigger `delete`  DML () rollback segement 

**DML  DDL **

- DML Data Manipulation Language
- DDL Data Definition Language DML  DML DDL DBA

`select``select` DQLData Query Language

### 

`drop` > `truncate` > `delete`

- `delete``binlog`
- `truncate``delete`
- `drop`

Tips

## ?

1. **** : 
2. **** :  E-R  E-R 
3. **** :  E-R  E-R 
4. **** : 
5. **** : 
6. **** : 

## 

- 
- 
-