How do I display a specific error message to the user when a stored procedure encounters a constraint violation?

To display a specific error message for constraint violations, use the `RAISERROR` function within the stored procedure. You can specify the severity level (e.g., 16 for error), state, and the message itself. For example: `RAISERROR('Invalid data entered. Please correct.', 16, 1, @InvalidData);`. The severity level determines how the error is handled. The state and message provide more context for debugging. Consider using parameterized queries to prevent SQL injection vulnerabilities when constructing the error message.