Database mistakes.md

A business-relevant field as a primary key is a mistake.

- the value can change (which lad to entity no longer identified by that field)
- you don't have access to that field
- solution: create a new field just for the primary key (Surrogate key).

Storing the age

• age is need to re calculated when ever it is needed

Referential integrity

Storing optional types of data in different columns