# Database HW

## Problem 1
### ER Model

### Relational Model

create table Professor (
    pid integer primary key,
    pname varchar(30) not null,
    rank integer
);
create table Project (
    project_number integer primary key,
    sponsor varchar(30) not null,
    start_time date not null,
    end_time date not null,
    budget integer not null,
    pid integer,
    foreign key (pid) references professor 
);
create table Student (
    sid integer primary key,
    sname varchar(30) not null,
    degree varchar(15),
    pid integer,
    foreign key (pid) references professor
);
create table participate(
    pid integer,
    project_num integer,
    foreign key (pid) references student,
    foreign key (project_num) references project,
    start_date date,
    end_date date,
    payment integer,
    primary key (pid, project_num)
);

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## Problem2

| <u>fourm_name</u> | popularity |
| -------- | -------- |
| Gossiping | 100 |
| Joke | 23 |

| <u>fourm_name</u> | <u>post_id</u> | title | article |
| -------- | -------- | -------- |------- |
| Gossiping | 131 | Girlfriend |How can I get girlfriend ?|
| Gossiping | 252 | Firends | I don't have a friend...|
| Joke | 46 | Knock | Knock! Knock! ... |
| Joke | 151 | Santa Claus | Hold! Hold! Hold! |

|<u>rid</u>| fourm_name | post_id |reply|
|---------| -------- | -------- | ----|
|1| Gossiping | 131 |Haha|
|2| Gossiping | 131 | I don't know |
|3| Gossiping | 252 |Haha|
|4| Gossiping | 252 |I can be|
|5| Gossiping | 252 |QQ|
|6| Joke | 46 | Then |
|7| Joke | 46 | What's the point |
|8| Joke | 151 | XDD |