Introduction
CHECK constraints with a simple condition
CHECK constraints with complex conditions
Adding CHECK constraints to existing tables
Instruction
Let's get started. Take a look at the following example:
CREATE TABLE video_game ( id GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY, name varchar(32) UNIQUE NOT NULL, genre varchar(32) NOT NULL, studio varchar(32), multiplayer boolean, hours integer CHECK (hours > 0), price decimal(5, 2) CHECK (price > 0) );
As you can see, we added the keyword CHECK to two columns, followed by a logical condition inside parentheses. For example, the price column value cannot be 0 or less because of the condition we set (price > 0). The database will ensure that this condition is always met.
Exercise
Run the template code to create the video_game table with the new constraint CHECK. The new columns which may require some explanation are:
multiplayer– This column tells us whether a specific game has a multiplayer mode.hours– This column stores the estimated number of hours necessary to complete the game.
