Introduction
UNIQUE
NOT NULL
CHECK
DEFAULT
Instruction
Alright. We'll start off with UNIQUE. This constraint means that the values in a given column must be... well, unique. In other words, you can't have more than one row with the same value in such columns. Take a look at our instruction:
CREATE TABLE board_game (
id IDENTITY PRIMARY KEY,
name varchar(32) UNIQUE,
genre varchar(32),
min_players int,
min_age int,
price decimal(5,2)
);
As you can see, the column name has the UNIQUE constraint. It is placed after the type of the column.
Exercise
Our users added some games to the table board_game. Select all the information from the table and study the column name.
As you will see, all the values are unique and each of them appears only once.
Stuck? Here's a hint!
Type
SELECT * FROM board_game;
