To ensure that data values follow defined rules for formatting, range, and value using check and default constraints, you use domain integrity.

The check constraint is used to ensure that all values in a column are within a range of values. This type of key can be applied to any data type and is used to ensure that values aren't invalid. A check constraint is enforced with user-defined conditions and evaluates as either true or false. You can define a check constraint on a single column or a combination of columns in a table.

The following screenshot shows an example of a table where a check constraint would make sense on the inducted column. A player can either be inducted into the hall of fame or not. In this case, you could create a check constraint that only allows Y or N in that field. If the value isn't Y or N, then the row can't be updated or inserted:

The following screenshot shows an example of a table where a check constraint can be applied to multiple columns. For instance, you wouldn't want deathYear to be a year before the birthYear, so you can set a check constraint that will only allow you to add or update a birthYear or deathYear that follows a check constraint like birthYear < deathYear:

To ensure that all rows in a column have a value, you use a default constraint. This type of key can be applied to any data type. A default constraint assigns a default value to a field. This is used to avoid having a null value for a field if a user doesn't specify a value.

The following screenshot shows an example of a table where a default constraint could make sense on the ab column:

A player can be in a game without having any at-bats. In this case, you could create a default constraint that sets the ab column to 0 if the user provides no value.