N:M or 1:M relationship?

Question

[Swimming bird]

Hello! I'm working on the database design of NGS pipeline focused in diagnostics. I'm working with MySQL. I created a table for the samples. At first, I thought that it would be a good idea to create a column for the index sequence used by the sequencer but the problem is that in some cases the samples have 2 indexes and this breaks the First Normal Form.

As a result, I decided to create an extra table for indexes but in this case I don't know if the relationship is N:M or 1:N considering that an index can be used for different samples in different sequencing runs and a sample can have 1 or 2 indexes or more if we consider that the samples can be sequenced twice in case of an error.

Answer 1

[Jean-Karim Heriche]

N:M means a many-to-many relation and 1:N means a one-to-many relation. Since a sample can have multiple indexes, the index side is N and since an index can be used for more than one sample then the sample side should be >=1 so M. So you need to represent a N:M/many-to-many relationship.

[Swimming bird]

I think the same but I found an example with products and two columns of colours and in that case the relationship is considered as 1:M although a colour can be present in several products.