Introduction
UNIQUE
NOT NULL
CHECK
DEFAULT
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.
