Oracle Constraints: Types & Data Integrity

In Oracle databases, constraints are rules used to ensure data integrity and consistency. Constraints can be applied at the column level or at the table level, with common types including:

1. Primary key constraint: Ensures the uniqueness of a column or group of columns, and does not allow the column or group to contain NULL values.
2. Foreign key constraints ensure that the values of a foreign key in one table can only reference the primary key values in another table, used to maintain the association between tables.
3. The only constraint: ensure that all values in a column or group of columns are unique.
4. Non-null constraint: ensure that a column does not allow for NULL values.
5. Check Constraint: Setting a condition that only allows data to be inserted or updated if it meets the criteria.
6. Default constraint: Define a default value for a column, so that if a value is not specified for that column when inserting a new record, the default value will be used.

By using these constraints, it is possible to effectively ensure the integrity and consistency of data in the database, preventing any illegal data from being inserted or updated.