SQL Constraints & Data Integrity

Constraints

• NOT NULL Constraint: Ensures that a column cannot have NULL value.
• DEFAULT Constraint: Provides a default value for a column when none is specified.
• UNIQUE Constraint: Ensures that all values in a column are different.
• PRIMARY Key: Uniquely identified each rows/records in a database table.
• FOREIGN Key: Uniquely identified a rows/records in any another database table.
• CHECK Constraint: The CHECK constraint ensures that all values in a column satisfy certain conditions.
• INDEX: Use to create and retrieve data from the database very quickly

Data Integrity

• Entity Integrity: There are no duplicate rows in a table.
• Domain Integrity: Enforces valid entries for a given column by restricting the type, the format, or the range of values.
• Referential Integrity: Rows cannot be deleted which are used by other records.
• User-Defined Integrity: Enforces some specific business rules that do not fall into entity, domain, or
  referential integrity.