Question

I’m a bit puzzled to something we got here at the office. We have the same database structure for Oracle and MySQl.

Using Data Modeler we generated the ER diagram of both, and the MySQL DB is missing relationships.

The reason of that, according our DBA, is that those tables are MyISAM to favor full text indexing. But we do use a lot of relations on those tables too, which is why the Oracle version does show them.

Whats right and wrong on our DBs?

Answer 1

I’m not exactly sure what your question is. If you clarify, I’ll try and provide a better answer.

Anyway, MySQL has multiple storage engines. MyISAM and InnoDB are two of them (there are others). Each engine has different properties, such as performance, features, etc.

Here’s the MySQL docs on foreign keys:

For storage engines other than InnoDB, MySQL Server parses the FOREIGN
KEY syntax in CREATE TABLE statements, but does not use or store it.

and

MySQL gives database developers the choice of which approach to use.
If you don’t need foreign keys and want to avoid the overhead
associated with enforcing referential integrity, you can choose
another storage engine instead, such as MyISAM. (For example, the
MyISAM storage engine offers very fast performance for applications
that perform only INSERT and SELECT operations …).

In other words, if you use MyISAM, you’ll have to take care of foreign key checks yourself. If foreign key checks are very important to you, then I would indeed strongly suggest using InnoDB.