多项选择题

Which three statements about subqueries are true?（）

A. A single row subquery can retrieve only one column and one row.
B. A single row subquery can retrieve only one row but many columns.
C. A multiple row subquery can retrieve multiple rows and multiple columns.
D. A multiple row subquery can be compared by using the ">" operator.
E. A single row subquery can use the IN operator.
F. A multiple row subquery can use the "=" operator.

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多项选择题When should you create a role? （）

A. To simplify the process of creating new users using the CREATE USER xxx IDENTIFIED by yyy statement.
B. To grant a group of related privileges to a user.
C. When the number of people using the database is very high.
D. To simplify the process of granting and revoking privileges.
E. To simplify profile maintenance for a user who is constantly traveling.

单项选择题Which clause would you use in a SELECT statement to limit the display to those employees whose salary is greater then 5000? （）

A. ORDER BY SALARY > 5000
B. GROUP BY SALARY > 5000
C. HAVING SALARY > 5000
D. WHERE SALARY > 5000

单项选择题Examine the structure of the EMPLOYEES table: EMPLOYEE_ID NUMBER Primary Key FIRST_NAME VARCHAR2(25) LAST_NAME VARCHAR2(25) DEPARTMENT_ID NUMBER SALARY NUMBER What is the correct syntax for an inline view? （）

A. SELECT a.last_name, a.salary, a.department_id, b.maxsal FROM employees a, (SELECT department_id, max(salary)maxsal FROM employees GROUP BY department_id) b WHERE a.department_id = b.department_id AND a.salary < b.maxsal;
B. SELECT a.last name, a.salary, a.department_id FROM employees a WHERE a.department_id IN (SELECT department_id FROM employees b GROUP BY department_id having salary = (SELECT max(salary) from employees))
C. SELECT a.last_name, a.salary, a.department_id FROM employees a WHERE a.salary = (SELECT max(salary) FROM employees b WHERE a.department _ id = b.department _ id);
D. SELECT a.last_name, a.salary, a.department_id FROM employees a WHERE (a.department_id, a.salary) IN (SELECT department_id, a.salary) IN (SELECT department_id max(salary) FROM employees b GROUP BY department_id ORDER BY department _ id);

单项选择题Which SQL statement generates the alias Annual Salary for the calculated column SALARY*12? （）

A. SELECT ename, salary*12 'Annual Salary' FROM employees;
B. SELECT ename, salary*12 "Annual Salary" FROM employees;
C. SELECT ename, salary*12 AS Annual Salary FROM employees;
D. SELECT ename, salary*12 AS INITCAP("ANNUAL SALARY") FROM employees

单项选择题In which scenario would index be most useful? （）

A. The indexed column is declared as NOT NULL.
B. The indexed columns are used in the FROM clause.
C. The indexed columns are part of an expression.
D. The indexed column contains a wide range of values.