单选题以下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
单选题
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
参考解析
解析：
暂无解析
相关考题：
在SQL Server 2000中，设有职工表(职工号， 职工名， 电子邮箱)，现要限制电子邮箱的最后几位的取值为“@abc.com”，且“@”前至少有一位字符。下列添加约束的语句正确的是A．ALTER TABLE职工表 ADD CONSTRAINT chk_email CHECK(电子邮箱LIKE '_%@abc.com')B．ALTER TABLE职工表 ADD CONSTRAINT chk_email CHECK(电子邮箱 = '_%@abc.com')C．ALTER TABLE职工表 ADD CONSTRAINT chk_email CHECK(电子邮箱LIKE '_@abc.com')D．ALTER TABLE职工表 ADD CONSTRAINT chk_email CHECK(电子邮箱 = '_@abc.com')
为“选课”表增加一个“等级”字段，其类型为C、宽度为2，正确的SQL命令是（ ）。A.ALTER TABLE选课ADD nELD等级C(2)B.ALTER TABLE选课ALTER FIELD等级C(2)C.ALTER TABLE选课ADD等级C(2)D.ALTER TABLE选课ALTER等级C(2)
You need to modify the STUDENTS table to add a primary key on the STUDENT_ID column. The table is currently empty. Which statement accomplishes this task?() A. ALTER TABLE students ADD PRIMARY KEY _ id;B. ALTER TABLE students ADD CONSTRAINT PRIMARY KEY (student_id);C. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY student_id;D. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id);E. ALTER TABLE students MODIFY CONSTRAINT stud_id_pk PRIMARY KEY (student_id);
Which statement adds a constraint that ensures the CUSTOMER_NAME column of the CUSTOMERS table holds a value?() A. ALTER TABLE customers ADD CONSTRAINT cust_name_nn CHECK customer_name IS NOT NULL;B. ALTER TABLE customers MODIFY CONSTRAINT cust_name_nn CHECK customer_name IS NOT NULL;C. ALTER TABLE customers MODIFY customer_name CONSTRAINT cust_name_nn NOT NULL;D. ALTER TABLE customers MODIFY customer_name CONSTRAINT cust_name_nn IS NOT NULL;E. ALTER TABLE customers MODIFY name CONSTRAINT cust_name_nn NOT NULL;F. ALTER TABLE customers ADD CONSTRAINT cust_name_nn CHECK customer_name NOT NULL;
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);
Which syntax turns an existing constraint on? () A. ALTER TABLE table_name ENABLE constraint_name;B. ALTER TABLE table_name STATUS = ENABLE CONSTRAINT constraint _ name;C. ALTER TABLE table_name ENABLE CONSTRAINT constraint _ name;D. ALTER TABLE table_name TURN ON CONSTRAINT constraint _ name;
The EMPLOYEES table has these columns:Management wants to add a default value to the SALARY column. You plan to alter the table by using this SQL statement:What is true about your ALTER statement?() A. Column definitions cannot be altered to add DEFAULT values.B. A change to the DEFAULT value affects only subsequent insertions to the table.C. Column definitions cannot be altered at add DEFAULT values for columns with a NUMBER data type.D. All the rows that have a NULL value for the SALARY column will be updated with the value 5000.
为“部门”表增加一个“人数”字段，类型为整型，正确的命令是( )。A．ALTER TABLE 部门 ALTER 人数 IB．ALTER TABLE 部门 ALTER FIELDS 人数 IC．ALTER TABLE 部门 ADD 人数 ID．ALTER TABLE 部门 ADD FIELDS 人数 I
给student表增加一个“平均成绩”字段(数值型，总宽度6，2位小数)的SQL命令是A．ALTER TABILE student ADD平均成绩N(6，2)B．ALTER TABLE student ADD平均成绩D(6，2)C．ALTER TABLE student ADD平均成绩E(6，2)D．ALTER TABLE student ADD平均成绩Y(6，2)
给student表增加一个“平均成绩”字段(数值型，总宽度6，2位小数)的SQL命令是（ ）。A.ALTER TABLE student ADD平均成绩N(6，2)B.ALTER TABLE student ADD平均成绩D(6，2)C.ALTER TABLE student ADD平均成绩E(6，2)D.ALTER TABLE student ADD平均成绩Y(6，2)
为表TEST中ID列添加主键约束的语法是（）A、ALTER TABLE TEST CHANGE（ ID INT PRIMARY KEY）B、ALTER TABLE TEST ADD（ ID INT PRIMARY KEY）C、ALTER TABLE TEST MODIFY（ ID INT PRIMARY KEY）D、ALTER TABLE TEST ADD CONSTRAINT PK PRIMARY KEY （ID）
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）
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）
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
在SQL Server中，修改表中列定义的正确的SQL语句是（）。A、ALTER TABLE 表名 ALTER COLUMN 列名 数据类型B、ALTER TABLE 表名 ALTER 列名 数据类型C、ALTER TABLE MODIFY COLUMN 列名 数据类型D、ALTER TABLE 表名 ADD 列名 数据类型
Which syntax turns an existing constraint on?（）A、ALTER TABLE table_name ENABLE constraint_name;B、ALTER TABLE table_name STATUS = ENABLE CONSTRAINT constraint_name;C、ALTER TABLE table_name ENABLE CONSTRAINT constraint_name;D、ALTER TABLE table_name STATUS ENABLE CONSTRAINT constraint_name;E、ALTER TABLE table_name TURN ON CONSTRAINT constraint_name;
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);
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
You need to modify the STUDENTS table to add a primary key on the STUDENT_ID column. The table is currently empty.Which statement accomplishes this task?（）A、ALTER TABLE students ADD PRIMARY KEY student_id;B、ALTER TABLE students ADD CONSTRAINT PRIMARY KEY (student _ id);C、ALTER TABLE students ADD CONSTRAINT stud _ id _pk PRIMARY KEY (student _ id);D、ALTER TABLE students MODIFY CONSTRAINT stud _ id _pk PRIMARY KEY (student _ id);
Examine the following statement that is used to modify the constraint on the SALES table： SQL ALTER TABLE SALES MODIFY CONSTRAINT pk DISABLE VALIDATE； Which three statements are true regarding the above command（）A、The constraint remains valid.B、The index on the constraint is dropped.C、It allows the loading of data into the table using SQL*Loader.D、New data conforms to the constraint， but existing data is not checkedE、It allows the data manipulation on the table using INSERT/UPDATE/DELETE SQL statements.
Which syntax turns an existing constraint on? （）A、ALTER TABLE table_name ENABLE constraint_name;B、ALTER TABLE table_name STATUS = ENABLE CONSTRAINT constraint _ name;C、ALTER TABLE table_name ENABLE CONSTRAINT constraint _ name;D、ALTER TABLE table_name TURN ON CONSTRAINT constraint _ name;
You need to modify the STUDENTS table to add a primary key on the STUDENT_ID column. The table is currently empty.Which statement accomplishes this task?（）A、ALTER TABLE students ADD PRIMARY KEY student_id;B、ALTER TABLE students ADD CONSTRAINT PRIMARY KEY (student_id);C、ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY student_id;D、ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id);E、ALTER TABLE students MODIFY CONSTRAINT stud_id_pk PRIMARY KEY (student_id);
多选题Examine the following statement that is used to modify the primary key constraint on the SALES table： SQL ALTER TABLE SALES MODIFY CONSTRAINT pk DISABLE VALIDATE； Which three statements aretrue regarding the above command（）AThe constraint remains valid.BThe index on the constraint is dropped.CIt allows the loading of data into the table using SQL *Loader.DNew data conforms to the constraint， but existing data is not checked.EIt allows the data manipulation on the table using INSERT/UPDATE/DELETE SQL statements.
单选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（）AALTER TABLE salary ADD CONSTRAINT fk_employee_id_01 FOREIGN KEY（employee_id）REFERENCES employees（employee_id）BALTER TABLE salary ADD CONSTRAINT fk_employee_id_ FOREIGN KEY BETWEEN salary（employee_id）AND employees（employee_id）CALTER TABLE salary FOREIGN KEY CONSTRAINT fk_employee_id_REFERENCES employees（employee_id）DALTER TABLE salary ADD CONSTRAINT fk_employee_id_FOREIGN KEY salary（employee_id）=employees（employee_id）
单选题The EMPLOYEES table has these columns: LAST NAME VARCHAR2(35) SALARY NUMBER(8,2) HIRE_DATE DATE Management wants to add a default value to the SALARY column. You plan to alter the table by using this SQL statement: ALTER TABLE EMPLOYEES MODIFY ( SALARY DEFAULT 5000); What is true about your ALTER statement?（）AColumn definitions cannot be altered to add DEFAULT values.BA change to the DEFAULT value affects only subsequent insertions to the table.CColumn definitions cannot be altered at add DEFAULT values for columns with a NUMBER data type.DAll the rows that have a NULL value for the SALARY column will be updated with the value 5000.
多选题Examine the following statement that is used to modify the constraint on the SALES table： SQL ALTER TABLE SALES MODIFY CONSTRAINT pk DISABLE VALIDATE； Which three statements are true regarding the above command（）AThe constraint remains valid.BThe index on the constraint is dropped.CIt allows the loading of data into the table using SQL*Loader.DNew data conforms to the constraint， but existing data is not checkedEIt allows the data manipulation on the table using INSERT/UPDATE/DELETE SQL statements.
单选题The EMPLOYEES table has these columns:LAST_NAME VARCHAR2(35) SALARY NUMBER(8,2) HIRE_DATE DATEManagement wants to add a default value to the SALARY column. You plan to alter the table by using this SQL statement:ALTER TABLE EMPLOYEES MODIFY (SALARY DEFAULT 5000);Which is true about your ALTER statement?（）AColumn definitions cannot be altered to add DEFAULT values.BA change to the DEFAULT value affects only subsequent insertions to the table.CColumn definitions cannot be altered to add DEFAULT values for columns with a NUMBER data type.DAll the rows that have a NULL value for the SALARY column will be updated with the value 5000.