先試後買

A. NULL values are not allowed in relational databases.

B. NULL values represent missing or unknown data.

C. NULL values are treated as empty strings.

D. NULL values are treated as zero.

A. A NATURAL JOIN without specifying join conditions

B. An OUTER JOIN with NULL values

C. An INNER JOIN without specifying join conditions

A. All department IDs from the employees table

B. Department IDs that exist in both the departments and employees tables

C. All department IDs from the departments table

D. Department IDs that exist only in the employees table

A. FROM

B. GROUP BY

C. WHERE

D. SELECT

A. CREATE ROLE role_name;

B. ADD ROLE role_name;

C. CREATE NEW ROLE role_name;

A. Employees and their managers' IDs

B. All employees and their IDs

C. Employees who have managers

D. Employees who do not have managers

A. INNER JOIN

B. CROSS JOIN

C. OUTER JOIN

D. SELF JOIN