Data constraints on a column are the limits put on the values the data can have.
There are four types of data constraints:
(1) domain constraints, which define a limited set of values for the column,
(2) range constraints, which specify that the values must fall within a certain range,
(3) intrarelation constraints, which define what values the column can have based on values of other columns in the same table, and
(4) interrelation constraints, which define values the column can have based on values of columns in other tables.