Constraints, Rules, Defaults, and Triggers

Table columns have properties other than just data type and size. The other properties form an important part of the support for ensuring the integrity of data in a database.

• Data integrity refers to each occurrence of a column having a correct data value.

  The data values must be of the right data type and in the correct domain.

• Referential integrity indicates that the relationships between tables have been properly maintained.

  Data in one table should only point to existing rows in another table; it should not point to rows that do not exist.

Objects used to maintain both types of integrity include:

• Constraints
• Rules
• Defaults
• Triggers