In an off-hand comment on this question about storing PHP objects in a MySQL database I mentioned that it is probably not a good idea to do so.
My reasoning is that MySQL is explicitly a relational DBMS, and that it doesn't make sense to force it to be something else, as it will not be optimize for that.
I would assume that it would severely limit the power of SQL - every action such as combining data from different tables would now be moved to the application layer -, and I would assume that it will lead to a rather significant loss of performance - the whole object would now need to be fetched each time, and so on.
The OP of that question said that their teacher still recommended storing whole objects in MySQL - and there are multiple questions about this on stackoverflow, so I'm assuming they are not the only one doing it - , so I'm wondering if there are indeed any advantages to this approach, and if I correctly identified the downsides of this approach.
Note that I'm not asking about the benefits of NoSQL / Object DBMS, but about (mis)using a relational database to store objects.