What is trigger in SQL?

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What is a Trigger in SQL?

1. Definition:

• Explanation:
  • A trigger in SQL is a set of instructions or code that automatically initiates an action when a specific event occurs on a particular table or view.
• Key Elements:
  • Triggers are associated with INSERT, UPDATE, DELETE operations and are executed before or after these operations.

2. Types of Triggers:

• Before Triggers:

  • Executed before the triggering event (INSERT, UPDATE, DELETE).
  • Used for validation or to modify values before they are written to the database.

• After Triggers:

  • Executed after the triggering event.
  • Suitable for tasks like updating related tables or generating additional logs.

3. Use Cases and Applications:

• Data Validation:

  • Triggers are commonly used for enforcing data integrity through validation checks.
  • Example: Ensuring that a product's quantity is not negative after an order is placed.

• Auditing and Logging:

  • Triggers can be employed for tracking changes to specific columns or tables.
  • Example: Creating an audit trail to monitor user actions.

• Cascade Operations:

  • Triggers facilitate cascading actions across related tables.
  • Example: Updating a corresponding order total when a line item is modified.

4. Syntax and Structure:

• Example:
  sql