Constraints, Rules, Defaults, and Triggers

Table columns have properties other than data type and size. These other properties are an important part in 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