Introduction
UNIQUE
NOT NULL
CHECK
18. CHECK - Introduction
DEFAULT
Summary

Instruction

Good, so much for NOT NULL. We're now going to proceed to the next constraint and our next type of game. Take a look the following example:

CREATE TABLE video_game (
    id IDENTITY PRIMARY KEY,
    name varchar(32) UNIQUE NOT NULL,
    genre varchar(32) NOT NULL,
    studio varchar(32),
    multiplayer boolean,
    hours int CHECK hours > 0,
    price decimal(5,2) CHECK price > 0
);

As you can see, we added the keyword CHECK for some columns, followed by a logical condition. So, for example the column price cannot be equal to or lower than 0 because of the condition we set (price > 0). The database will ensure that the condition is always met.

Exercise

Run the template code to create our new table video_game with the new constraint CHECK. The new columns here which may require some explanation are:

  • multiplayer - this column tells us whether a specific game provides a multiplayer mode,
  • hours - this column provides the estimated number of hours necessary to complete the game.

Console

Code editor

Result

TableConsole