以下SQL命令执行什么操作（） ALTER TABLE employees ADD CONSTRAINT emp_manager_fk FOREIGN KEY(manager_id) REFERENCES employees(employee_id).A、更改employees表并禁用emp_manager_fk约束条件B、向EMPLOYEES表添加FOREIGN KEY约束条件，要求经理必须已是雇员C、向EMPLOYEES表添加FOREIGN KEY约束条件，要求经理标识应匹配每个雇员标识D、更改emp

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以下SQL命令执行什么操作（） ALTER TABLE employees ADD CONSTRAINT emp_manager_fk FOREIGN KEY(manager_id) REFERENCES employees(employee_id).

A、更改employees表并禁用emp_manager_fk约束条件
B、向EMPLOYEES表添加FOREIGN KEY约束条件，要求经理必须已是雇员
C、向EMPLOYEES表添加FOREIGN KEY约束条件，要求经理标识应匹配每个雇员标识
D、更改employees表并添加FOREIGN KEY约束，要求每个雇员标识必须唯一

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第1题

Which statement explicitly names a constraint? ()A. ALTER TABLE student_grades ADD FOREIGN KEY (student_id) REFERENCES students (student_id);B. ALTER TABLE student_grades ADD CONSTRAINT NAME = student_id_fk FOREIGN KEY (student_id) REFERENCES students (student_id);C. ALTER TABLE student_grades ADD CONSTRAINT student_id_fk FOREIGN KEY (student_id) REFERENCES students (student_id);D. ALTER TABLE student grades ADD NAMED CONSTRAINT student_id_fk FOREIGN KEY (student_id) REFERENCES students (student_id);E. ALTER TABLE student grades ADD NAME student_id_fk FOREIGN KEY (student_id) REFERENCES students (student_id);

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第2题

Examine the data in the EMPLOYEES and DEPARTMENTS tables:Also examine the SQL statements that create the EMPLOYEES and DEPARTMENTS tables:On the EMPLOYEES table, EMPLOYEE_ID is the primary key.MGR_ID is the ID of managers and refers to the EMPLOYEE_ID.DEPT_ID is foreign key to DEPARTMENT_ID column of the DEPARTMENTS table.On the DEPARTMENTS table, DEPARTMENT_ID is the primary key.Examine this DELETE statement:What happens when you execute the DELETE statement?（）A. Only the row with department ID 40 is deleted in the DEPARTMENTS table.B. The statement fails because there are child records in the EMPLOYEES table with department ID 40.C. The row with department ID 40 is deleted in the DEPARTMENTS table. Also the rows with employee IDs 110 and 106 are deleted from the EMPLOYEES table.D. The row with department ID 40 is deleted in the DEPARTMENTS table. Also the rows with employee IDs 106 and 110 and the employees working under employee 110 are deleted from the EMPLOYEES table.E. The row with department ID 40 is deleted in the DEPARTMENTS table. Also all the rows in the EMPLOYEES table are deleted.F. The statement fails because there are no columns specifies in the DELETE clause of the DELETE statement.

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第3题

下列哪个FOREIGN KEY约束条件关键字用来标识表和父表中的列？（）A、RESEMBLESB、ON DELETE CASCADEC、REFERENTIALD、REFERENCES

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第4题

评估以下语句： ALTER TABLE employees ADD CONSTRAINT employee_id PRIMARY KEY; 该语句将返回以下哪种结果（）A、将返回语法错误B、将向EMPLOYEES表添加约束条件C、将改写EMPLOYEES表的一个现有约束条件D、将启用EMPLOYEES表的一个现有约束条件

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第5题

您在公司的数据库中成功创建了名为SALARY的表。您现在要通过向引用EMPLOYEES表的匹配列的SALARY表添加FOREIGNKEY约束条件来建立EMPLOYEES表与SALARY表之间的父/子关系。尚未向SALARY表添加任何数据。应执行以下哪条语句（）A、ALTER TABLE salary ADD CONSTRAINT fk_employee_id_01 FOREIGN KEY（employee_id）REFERENCES employees（employee_id）B、ALTER TABLE salary ADD CONSTRAINT fk_employee_id_ FOREIGN KEY BETWEEN salary（employee_id）AND employees（employee_id）C、ALTER TABLE salary FOREIGN KEY CONSTRAINT fk_employee_id_REFERENCES employees（employee_id）D、ALTER TABLE salary ADD CONSTRAINT fk_employee_id_FOREIGN KEY salary（employee_id）=employees（employee_id）

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第6题

要向雇员表中的部门标识列添加FOREIGNKEY约束条件以引用部门表中的标识列，应该使用哪个语句（）A、ALTER TABLE雇员MODIFY COLUMN dept_id_fk FOREIGN KEY（部门标识）REFERENCES部门（部门标识）B、ALTER TABLE雇员ADD CONSTRAINT dept_id_fk FOREIGNKEY（部门标识）REFERENCES部门（部门标识）C、ALTER TABLE雇员ADD FOREIGN KEY CONSTRAINT dept_id_fk ON（部门标识）REFERENCES部门（部门标识）D、ALTER TABLE雇员ADD FOREIGN KEY 部门（部门标识）REFERENCES（部门标识）

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第7题

删除PRIMARYKEY约束条件及其所有依赖约束条件的语法是什么（）A、ALTER TABLE table_name DROP CONSTRAINT constraint_name CASCADEB、ALTER TABLE table_name DROP CONSTRAINT FOREIGN KEY CASCADEC、DROP CONSTRAINT table_name（constraint_name）D、ALTER TABLE table_name DROP CONSTRAINT constraint_name

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