Unindexed foreign keys many-to-many table

[thedevdavid]

Performance advisor reports unindexed foreign keys for a junction table. Is this necessary if the junction table has a composite primary key as a unique index?

[encima]

This depends on query usage you have, the index you get "for free" is a composite on tracks_id and playlist_id but you may have queries that are just querying the tracks_id in the table or, possibly, querying both but in a different order such that it is not used.

The advice is not wrong but I do see that this may also result in over-indexing. Not sure this is a bug but we could move it to discussions to see what others think?