Mr. Froasty, >From your note, it sounds like you want to use foreign keys; as Daniel pointed out. I think an example would be helpful here. The subject of foreign keys is bigger than a bread box so I'll just touch on the pieces I think you'll find helpful. There is all sorts of literature scattered about the web if you want to know more. Let's start with a fictional case: I work for a company with multiple departments each of which have one or more employees. I would like a relational data structure to capture departmental and employee information as well as preserve the relationship between the two. Make sense? I create two tables: `Department` and `Employee`. Each table has a primary key (as you illustrated in your example), which is unique per record. <important>I add a column in Employee that holds the primary key of the employee's associated department</important>. I then create a relation between the two tables to indicate there is a relationship. --Create the Department table CREATE TABLE Department ( IDDepartment INT NOT NULL AUTO_INCREMENT, Name VARCHAR(35), PRIMARY KEY (IDDepartment) ) ENGINE = InnoDB; --Create the Employee table and simultaneously the --relation to Department CREATE TABLE Employee ( IDEmployee INT NOT NULL AUTO_INCREMENT, idDepartment INT NOT NULL, Name VARCHAR(35), PRIMARY KEY (IDEmployee), INDEX IDX_idDepartment (idDepartment), FOREIGN KEY (idDepartment) REFERENCES Department(idDepartment) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE = InnoDB; MySQL can do all of this provided you're using the InnoDB storage engine. MySQL's documentation has some helpful information on the subject - see link below. http://dev.mysql.com/doc/refman/5.0/en/ansi-diff-foreign-keys.html With me so far? A few points specific to MySQL: (1) Whatever field you chose as your foreign key, needs an index. (2) You can add foreign keys after a table has been created using an ALTER statement. (3) The option ON DELETE CASCADE means that whenever the parent record (i.e., the department) is deleted the related employees will be deleted too. (4) The option ON UPDATE CASCADE means that whenver the parent's key record (i.e., the department) is updated the related foreign key record will be updated too. (5) There are options other than ON UPDATE and ON DELETE. Give'm a look. Good luck, and welcome to the DB development club. Cheers, Adam -----Original Message----- From: mrfroasty [mailto:mrfroasty@xxxxxxxxx] Sent: Thursday, November 27, 2008 5:19 AM To: php-db@xxxxxxxxxxxxx Subject: re:database tables relations advice I am quite new to database designs, I have a problem in my design...I can actually feel it, but I am not quite sure if there is a feature in mysql or I have to solve it with programming. Example: CREATE TABLE A ( user_id int(16) NOT NULL auto_increment, ..........other datas PRIMARY KEY (user_id) ); CREATE TABLE B ( user_id int(16) NOT NULL auto_increment, ..............other datas PRIMARY KEY (contact_id) ); Question: How can I declare that the user_id in my 1st table is related to user_id in the 2nd table...actually I prefer to have it exactly the same user_id in both tables....I think if those 2 entries are the same it will be great, but I am not sure how to achieve this. P:S -Ofcourse I know that I can extract it from TABLE A and save it in TABLE B....but is that a way to go???Because this issue arise in couple of tables in my data structure that I am tending to use in my application(web). -I also know that its possible to make just 1 big table with lots of columns....but I read its not a good database design... ----->>>>>please advice, running out of ideas :-( Thanks...... -- Extra details: OSS:Gentoo Linux-2.6.25-r8 profile:x86 Hardware:msi geforce 8600GT asus p5k-se location:/home/muhsin language(s):C/C++,VB,VHDL,bash Typo:40WPM url:http://mambo-tech.net -- PHP Database Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php -- PHP Database Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
