IMHO I think you will find that there is a balance between
the speed of opening and reading/writing several related
smaller tables connected by FK's, rather than one mega-sized
gigantic table.
How do you normalise a table without using FK's.
Your right, MySQL does not currently do any checking for
FK's, but this does not mean that you cannot still use them
in MyISAM tables.
Eg.
/* table to store quiz questions */
CREATE TABLE `quiz_question` (
`ID` mediumint UNSIGNED NOT NULL auto_increment,
`question_text` text NOT NULL,
PRIMARY KEY `ID` (`ID`)
) TYPE=MyISAM AUTO_INCREMENT=1;
/* table to store quiz answers */
CREATE TABLE `quiz_answer` (
`ID` mediumint UNSIGNED NOT NULL auto_increment,
`answer_text` text NOT NULL,
`status` enum('wrong', 'right') NOT NULL,
`questionID` mediumint UNSIGNED NOT NULL default '0',
PRIMARY KEY `ID` (`ID`),
KEY `questionID` (`questionID`)
) TYPE=MyISAM AUTO_INCREMENT=1;
/* table to track quiz questions with user answers */
CREATE TABLE `quiz_result` (
`ID` mediumint UNSIGNED NOT NULL auto_increment,
`user` char(32) NOT NULL default '',
`questionID` mediumint UNSIGNED NOT NULL default '0',
`answerID` mediumint UNSIGNED NOT NULL default '0',
PRIMARY KEY `ID` (`ID`),
KEY `questionID` (`questionID`),
KEY `answerID` (`answerID`)
) TYPE=MyISAM AUTO_INCREMENT=1;
So in the quiz_result table above questionID is a
column holding the primary key of each question_text column
in the quiz_question table. It is a foreign key.
answerID is a foreign key that points to the primary
key of the answer submitted by the user doing the quiz.
When the user has finished doing the quiz, the quiz_result
table is scanned for the user session ID, 'user', and then
the question and the user's chosen answer are picked from
the quiz_question and quiz_answer tables, using the foreign
keys in the result table.
I find it helps me to think of foreign keys as unique
pointers to rows in other related tables.
HTH
Keith
In theory, theory and practice are the same;
in practice they are not.
On Mon, 20 Mar 2006, Foo Ji-Haw wrote:
> To: [email protected]
> From: Foo Ji-Haw <[EMAIL PROTECTED]>
> Subject: Discussion: the efficiency in using foreign keys
>
> Hi all,
>
> This is a fundamental concept in RDBMS: the use of foreign keys in
> database design.
>
> I'd just like to poll the community here, on whether it is a best
> practice, or practically essential to 'link' related tables by use of
> foreign keys.
>
> For myself, I usually do all the validity checking when adding a new
> record that references a record id from another table. I understand that
> this may not be efficient because it becomes 2 database calls (and db
> calls are expensive in high-load environments).
>
> What are the advantages/ disadvantages in using foreign keys? In MySQL,
> this means one cannot use MyISAM. Do you place a lot of triggers as well?
>
> Thanks.
>
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