Representing M:N relationship in database

Question

Hi,
I have created three tables basically. They are as follows:
Table 1:
CREATE TABLE BOOKS
     ( ID CHAR(4) NOT NULL,
     TITLE VARCHAR(100),
     PRICE DECIMAL(5,3),
     ONSALE CHAR(2),
     YEAR CHAR(4),
DESCRIPTION VARCHAR(100),
INVENTORY CHAR(2),
PRIMARY KEY(ID));
Table 2:
CREATE TABLE AUTHORS
     ( AUTHID CHAR(4) NOT NULL,
FIRSTNAME VARCHAR(20),
SURNAME VARCHAR(20),
ORGANIZATION VARCHAR(19),
PRIMARY KEY(AUTHID));
// Since the above relationship is M:N we need to create a New table and I've done that below:
Table 3:
CREATE TABLE HAS_AUTHORS
     (BOOKID CHAR(4) NOT NULL,
AUTHORID CHAR(4) NOT NULL,
PRIMARY KEY(BOOKID,AUTHORID),
FOREIGN KEY(BOOKID) REFERENCES BOOKS(ID) on delete cascade,
FOREIGN KEY(AUTHORID) REFERENCES AUTHORS(AUTHID) on delete cascade);
Now My Question is:
Do I have to populate the HAS_AUTHORS table manually too or will the values I put into Table1 and Table 2 for ID and AUTHID be propagated to BOOKID and AUTHORID? It's probably a silly question but am a beginner.
Thanks.
Message was edited by:
user503246

Answer 1

I think table 3(relationship) is not need.
table 3 is just relation table.
BOOKS
# ID
# AUTOID <--- I define this new relation key
TITLE
PRICE
ONSALE
YEAR
DESCRIPTION
INVENTORY
| M
|
|
|
| 1
AUTHOR
# AUTOID
FIRSTNAME
SURNAME
ORGANIZATION
CREATE TABLE BOOKS
( ID CHAR(4) NOT NULL,
AUTOID CHAR(4) NOT NULL,
TITLE VARCHAR(100),
PRICE DECIMAL(5,3),
ONSALE CHAR(2),
YEAR CHAR(4),
DESCRIPTION VARCHAR(100),
INVENTORY CHAR(2),
PRIMARY KEY(ID)
FOREIGN KEY(AUTHORID) REFERENCES AUTHORS(AUTHID));
you have to add new foreign key in books table.
Message was edited by:
dokeun Kim