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 MySQL PS: 

## , , , ?

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



![](https://img-blog.csdnimg.cn/img_convert/e21120184e63406526a4e873cacd23f2.png)

## , , , , , , 

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

## ?

* **()** 
* **()** 

## 



> 
>
> :  student_id  student_id  student_id student_id ;  ; 



> 1. **** a. DELETE UPDATE, ; b. 
> 2. **** 
> 3. 
> 4. **** 
> 5. ......



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




##  ER 

>  ER 

**E-R ** -(Entity Relationship Diagram)  

 ER M: N1  11:11 1: N

![ER](https://img-blog.csdnimg.cn/img_convert/4717673e36966e0e4b33fccfd753f6ea.png)

 ER ()

![](https://img-blog.csdnimg.cn/img_convert/5897753dfb301dfa3a814ab06e718a5e.png)

## ?

**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 

****

* 1NF
* 2NF1NF 
* 3NF3NF  2NF  

## ?

 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 Languageinsertupdatedeleteselect
* 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. **** : 

## 

* 
* 
*