To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) TRUNCATE is a DDL command whereas DELETE is a DML command - This option is correct. TRUNCATE is a Data Definition Language (DDL) command used to delete all the rows from a table, while DELETE is a Data Manipulation Language (DML) command used to delete specific rows from a table.

Option B) TRUNCATE is much faster than DELETE - This option is partially correct. TRUNCATE is generally faster than DELETE because it does not generate any transaction logs and does not need to record individual row deletions. However, the exact performance difference may vary depending on the specific database system and the size of the table.

Option C) In case of TRUNCATE, Trigger doesn't get fired. But in DML commands like DELETE, Trigger gets fired - This option is correct. When you use TRUNCATE, triggers associated with the table are not fired. However, when you use DELETE, triggers associated with the table may get fired.

Option D) All of the above - This option is incorrect. The correct answer is A, as explained above.

The correct answer is A. TRUNCATE is a DDL command whereas DELETE is a DML command.

• Thanks
• Wrong explanation

To obtain the definition of a view, you can query the data dictionary view called USER_VIEWS. This view contains information about all the views owned by the current user.

Option A) Using the DESCRIBE command in the EMP_DEPT_VU view is incorrect. The DESCRIBE command is used to display the structure of a table, not a view.

Option B) Using the DEFINE VIEW command on the EMP_DEPT_VU view is incorrect. The DEFINE VIEW command is not a valid command in most database systems. It is not used to obtain the definition of a view.

Option C) Using the DESCRIBE VIEW command on the EMP_DEPT_VU view is incorrect. The DESCRIBE VIEW command is not a valid command in most database systems. It is not used to obtain the definition of a view.

Option D) Querying the USER_VIEWS data dictionary view to search for the EMP_DEPT_VU view is correct. The USER_VIEWS view contains information about all the views owned by the current user, including their definitions.

Therefore, the correct answer is D) Query the USER_VIEWS data dictionary view to search for the EMP_DEPT_VU view.

• Thanks
• Wrong explanation

To modify the view by adding a fourth column, MANAGER_ID, from the EMPLOYEES table, you need to use the CREATE OR REPLACE VIEW statement.

The correct answer is:

D. CREATE OR REPLACE VIEW emp_dept_vu AS SELECT employee_id, employee_name, department_name, manager_id FROM employees e, departments d WHERE e.department_id = d.department_id;

Explanation: Option A) ALTER VIEW emp_dept_vu (ADD manager_id NUMBER); - This option is incorrect because the ALTER VIEW statement does not have an ADD clause to add columns to an existing view.

Option B) MODIFY VIEW emp_dept_vu (ADD manager_id NUMBER); - This option is incorrect because there is no MODIFY VIEW statement in SQL to modify the structure of a view.

Option C) ALTER VIEW emp_dept_vu AS SELECT employee_id, employee_name, department_name, manager_id FROM employee e, departments d WHERE e.department_id = d.department_id; - This option is incorrect because the ALTER VIEW statement does not allow you to change the SELECT statement of the view.

Option D) CREATE OR REPLACE VIEW emp_dept_vu AS SELECT employee_id, employee_name, department_name, manager_id FROM employees e, departments d WHERE e.department_id = d.department_id; - This option is correct because the CREATE OR REPLACE VIEW statement allows you to create or modify a view. In this case, it creates a view called emp_dept_vu with the specified columns and queries the EMPLOYEES and DEPARTMENTS tables to retrieve the required data.

Therefore, the correct answer is option D.

• Thanks
• Wrong explanation