Amara K.

This "misunderstanding" comes from the way MySQL is used in certain very extensive CMS/CRM/eCommerce platforms and which derives directly from the limitations of MySQL when it was based on MyISAM. For example, in WooCommerce you can find the woocommerce_shipping_zones and woocommerce_shipping_zone_locations tables. In the latter there is a "zone_id" field which refers to the former, but in its definition you won't find any "FOREIGN KEY". In fact, if you download WooComerce and try to find any FOREIGN KEY in the definition of tables, you won't find any: A whole eCommerce platform in which referential integrity is not used. It's surprising, because a relational BBDD is something completely different: Your entity model is treated almost like a "mathematical model" based on sets and invariants. In these invariants, referential integrity plays a fundamental role A good design of entities implies a good knowledge of data normalization. The problem with an entity model is that it is too much like a mathematical model: it models a reality with unchangeable rules and, depending on its complexity, requires a lot of intellectual effort to integrate new elements into it. As a result, it has to respond to the needs of a market that is changing and evolving at breakneck speed. If you're one of those using a relational DBMS, but you're not using its strengths (you don't need referential integrity), then you've been a victim of misunderstanding and, possibly, a document-oriented DBMS would be a better fit.