Oracle Database 12c SQL OCA/OCP 1Z0-071题库(21-25题)

QUESTION 21

The BOOKS_TRANSACTIONS table exists in your database.

SQL>SELECT * FROM books_transactions ORDER BY 3;

What is the outcome on execution?

A. The execution fails unless the numeral 3 in the ORDER BY clause is replaced by a column name.

B. Rows are displayed in the order that they are stored in the table only for the three rows with the lowest values in the key column.

C. Rows are displayed in the order that they are stored in the table only for the first three rows.

D. Rows are displayed sorted in ascending order of the values in the third column in the table.

答案：D

解析：ORDER BY，注意点：

1. ORDER BY 可以通过名称引用，表达式和位置引用进行排序；
2. 默认升序(ASC)，相反的是DESC；
3. ORDER BY可以应用列别名，SELECT语句执行顺序见第二题解析；
4. ORDER BY排序中，A~Z~a~z升序，如果是字符型数字，则从第一个字符开始比较。NULL大于一切值

QUESTION 22

Examine the command:

SQL > ALTER TABLE books_transactions
						ADD CONCTRAINT fk_book_id FOREIGN KEY (book_id)
						REFERENCES books （book_id）on DELETE CASCADE;

What does ON DELETE CASCADE imply?

A. When the BOOKS table is dropped, the BOOK_TRANSACTIONS table is dropped.

B. When the BOOKS table is dropped, all the rows in the BOOK_TRANSACTIONS table are deleted but the table structure is retained.

C. When a row in the BOOKS table is deleted, the rows in the BOOK_TRANSACTIONS table whose BOOK_ID matches that of the deleted row in the BOOKS table are also deleted.

D. When a value in the BOOKS.BOOK_ID column is deleted, the corresponding value is updated in the BOOKS_TRANSACTIONS.BOOK_ID column.

答案：C

解析：约束ON DELETE :父表中的某行删除，子表中对应的行或多行也删除。

QUESTION 23

View the exhibit and examine the structure of the EMPLOYEES table.

Name                          NULL?                 Type
------------------              --------------         ----------------
EMPLOYEE_ID              NOT NULL           NUMBER(6)
FIRST_NAME                                           VARCHAR(20)
LAST_NAME              NOT NULL           VARCHAR(25)
HIRE_DATA              NOT NULL           DATE          
JOB_ID              NOT NULL            VARCHAR2(10)
SALARY                                                    NUMBER(10,2)
COMMISSION                                         NUMBER(6,2)
MANAGER_ID                                         NUMBER(6)
DEPARTMENT_ID                                   NUMBER(4)

You want to display all employees and their managers having 100 as the MANAGER_ID. You want the output in two columns: the first column would have the LAST_NAME of the managers and the second column would have LAST_NAME of the employees.

Which SQL statement would you execute?

A. SELECT m.last_name "Manager", e.last_name "Employee"
FROM employees m JOIN employees e
ON m.employee_id = e.manager_id
WHERE m.manager_id = 100;

B. SELECT m.last_name "Manager", e.last_name "Employee"
FROM employees m JOIN employees e
ON m.employee_id = e.manager_id
WHERE e.manager_id = 100;

C. SELECT m.last_name "Manager", e.last_name "Employee"
FROM employees m JOIN employees e
ON e.employee_id = m.manager_id
WHERE m.manager_id = 100;

D. SELECT m.last_name "Manager", e.last_name "Employee"
FROM employees m JOIN employees e
WHERE m.employee_id = e.manager_id AND e.manager_id = 100

答案：B

解析：自连接将同一个表中的列值与该列的值或是另一列的值进行比较，可以是内连接、外连接、等值连接或非等值连接

QUESTION 24

Which three statements are true about multiple-row subqueries?

A. They can contain a subquery within a subquery.

B. They can return multiple columns as well as rows.

C. They cannot contain a subquery within a subquery.

D. They can return only one column but multiple rows.

E. They can contain group functions and GROUP BY and HAVING clauses.

F. They can contain group functions and the GROUP BY clause, but not the HAVING clause.

答案：ABE

解析：子查询一些注意点：

1. 多行子查询可向父查询返回多行查询结果，对列无限制。关键字ANY/SOME ,父查询中的表达式需要满足子查询的任意结果（类似于OR），关键字ALL，父查询中的表达式需要满足子查询的所有结果（类似于AND）
2. 子查询可以使用GROUP BY 子句和ORDER BY 子句

QUESTION 25

Examine the structure of the EMPLOYEES table.

Name                          NULL?                 Type
------------------              --------------         ----------------
EMPLOYEE_ID              NOT NULL           NUMBER(6)
FIRST_NAME                                           VARCHAR(20)
LAST_NAME              NOT NULL           VARCHAR(25)
HIRE_DATA              NOT NULL           DATE          
JOB_ID              NOT NULL            VARCHAR2(10)
SALARY                                                    NUMBER(10,2)
COMMISSION                                         NUMBER(6,2)
MANAGER_ID                                         NUMBER(6)
DEPARTMENT_ID                                   NUMBER(4)

There is a parent/child relationship between EMPLOYEE_ID and MANAGER_ID.

You want to display the last names and manager IDs of employees who work for the same manager as the employee whose EMPLOYEE_ID is 123.

Which query provides the correct output?

A. SELECT e.last_name, m.manager_id
FROM employees e RIGHT OUTER JOIN employees m
on (e.manager_id = m.employee_id)
AND e.employee_id = 123;

B. SELECT e.last_name, m.manager_id
FROM employees e LEFT OUTER JOIN employees m
on (e.employee_id = m.manager_id)
WHERE e.employee_id = 123;

C. SELECT e.last_name, e.manager_id
FROM employees e RIGHT OUTER JOIN employees m
on (e.employee_id = m.employee_id)
WHERE e.employee_id = 123;

D. SELECT m.last_name, e.manager_id
FROM employees e LEFT OUTER JOIN employees m
on (e.manager_id = m.manager_id)
WHERE e.employee_id = 123;

答案：D

解析：参见23题解析。

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