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Introduction
UNIQUE
NOT NULL
17. NULL in ERD diagrams
CHECK
DEFAULT
Summary

## Instruction

Good! The last thing we want to show you about the NULL constraint is the way we mark it in ERD diagrams. Take a look:

Have you noticed the N signs on the right? This way, we can stress that a certain column may be NULL. Any other column without this mark is not allowed to be NULL.

## Exercise

Use the ERD diagram to write the proper instruction for creating the table.

### Stuck? Here's a hint!

Type

CREATE TABLE rpg_game (
id IDENTITY PRIMARY KEY,
name varchar(32) NOT NULL,
genre varchar(32) NOT NULL,
classes_no int NULL,
complexity int NULL,
min_players int NULL
);