Actual Phenomenon

Learned:

1. NULL semantics are unclear

2. Query is not easy to optimize

3. If it represents a null value, there can be other alternatives (logically)

   • VARCHAR(100) NOT NULL DEFAULT '';

   • INT NOT NULL DEFAULT 0;

Expected Phenomenon

1. I hope to understand the attitude towards NULL when designing a scheme (I remember reading an article saying that you should try: NOT NULL DEFAULT XXX)