Question

I have a database with some information which are repeated in some tables.

I want to know if it’s interesting to create a table with this information and in the other table, I put only the id.

It’s interesting because with this method I haven’t got redundance. But I will have to do many joints between my tables in my request, and I’m afraid my request will be more slow.

(I work with symfony if it changes something)

Answer 1

It sounds like the ‘information’ in question is data that makes up key values. If so, it sounds like the database designer likes to use natural keys and that you prefer to use surrogate keys.

First, these are both merely a question of style. If the natural key values are composite (i.e. involve more than one column) and are included in other columns for data integrity purposes then they are not redundant.

Second, as you have observed, when it comes to performance of surrogate keys you have to weigh the advantage of the more efficient data type (e.g. a single integer column) against the degrading performance of needing to write more JOINs. Note that using surrogates tends to make constraints more troublesome to write e.g. when the required values for a rule is in another table and you SQL product doesn’t support subqueries in CHECK constraints then you will need to use a trigger which degrades performance in a high activity environment.

Further consider that performance is not the only consideration e.g. using natural key values will tend to make the data more readable and therefore make the schema easier to maintain because the physical model will reflect the logical model more closely (surrogate keys do not appear in the logical model at all).