Introduction
Defining columns with UNIQUE
Adding and removing UNIQUE constraints
Instruction
All right! Let's get down to learning the UNIQUE constraint. Applying this constraint means that the values in a given column must be ... well, unique. In other words, each value in a UNIQUE column can only be used once. Here's how you specify the UNIQUE column when creating a table:
CREATE TABLE board_game ( id integer GENERATED ALWAYS AS IDENTITY PRIMARY KEY, name varchar(32) UNIQUE, genre varchar(32), min_players integer, min_age integer, price decimal(5, 2) );
As you can see, the name column has the UNIQUE constraint. It is placed after the type of the column.
Exercise
Our users added some games to the board_game table. Select all the information from the table and study the name column.
As you will see, all the values are unique: each of them appears only once.
