In the chapter introduction we promised to shed some light on how to choose your InnoDB primary key columns sensibly. Be advised that choosing good primary key columns is not an exact science—there are multiple aspects that influence this decision. Depending on your needs and preconditions you will want to prioritize them differently from one table to the next. Consider the following as general advice rather than hard rules that must be obeyed unconditionally.
In order to make reasonable decisions on primary key columns, it is important to have a very clear understanding of what the data looks like in the table at hand. If you already have existing data that is to be stored in an InnoDB table—for example in MyISAM format—it can be helpful to compare it with the criteria below.
If you are planning a new schema, you might have to guess about some characteristics of the future data. As is often the case, the quality of your...