I need to create a database using sql for my reviews site. I tried to use the on delete and on update constraints but I'm not sure if they are right. I created three tables a 'cars'(my review items) 'reviews'(holds the reviews) and a 'users' one. I linked cars_id and users_id with reviews table. I used on update cascade and on delete cascade for both. I'm not sure if that's right. Can someone help me understand them more?
SQL Confused over ON UPDATE and ON DELETE
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It is a matter of data modelling.
Ask yourself the question:
"If I delete a car, do I want to delete the relational records of other tables too?"
If YES put it to CASCADE etc.
Or:
"If I delete a user, do I want to delete his cars too?"
"If I delete a car, do I want do delete the corresponding user too?"
Maybe a good idea to read first here:
http://en.wikipedia.org/wiki/Relational_database
and then here: http://dev.mysql.com/doc/refman/5.1-olh/de/innodb-foreign-key-constraints.html