Column-level constraints

Constraints are rules that are enforced on data columns in a table. Whenever there is any change in data within a table, all the constraints are verified to make sure none is violated. If violated, the changes are rejected with the appropriate error message. Here is a list of column-level constraints:

• CHECK <condition>: A given condition is checked whenever a value is being inserted into the table. The condition is a Boolean expression that should evaluate to TRUE or NULL. If it returns FALSE for any value, the entire statement is rejected. It is possible to have multiple checks for the same column.

Here's an example to illustrate this:

CREATE TABLE user (
id INT NOT NULL, 
name STRING NOT NULL,
age INT NOT NULL CHECK (age > 18) CHECK (age < 65), 
PRIMARY KEY (id)
);

• DEFAULT: The DEFAULT value constraint is exercised whenever the INSERT statement doesn't explicitly insert a specific value or NULL for the column...