I'm working on trying to optimize a View SQL query and I noticed that the query being executed is using a join on a the entity_id field of a field table. I noticed that for some reason unbeknownst to me the entity_id field is not a primary key. The delta field is a primary key.
Can anyone enlighten me as to why this is the case? Can I safely tag entity_id as a primary key without incurring a wrath of unintended consequences? Thank you for your help.