Avoiding null values

When inserting a value into a table it can be always null in general. You can avoid this by marking a column as NOT NULL when defining the table. This is especially important when you want to set default values or restrict values on a column to unique values, because a null is always unique in SQL and column with a default value can still be null.

In order to mark a column as not nullable all we do is add NOT NULL after our type.

Remember to drop your table first

CREATE TABLE player
(
    id          INTEGER,
    player_name TEXT NOT NULL,
    last_online TIMESTAMP
);

When we now try to insert a NULL value into our player_name column we would get an error now.

INSERT INTO player(id, player_name, last_online)
VALUES (1, NULL, NULL)

When we insert this, we will get a nice error telling us that the player_name can not be null!