单选题Which constraint can be defines only at the column level? （）A UNIQUEB NOT NULLC CHECKD PRIMARY KEYE FOREIGN KEY

第1题：

第2题：

Which of the following scenarios will ensure that the value of the NEXT_STEPNO column in a given row of table TABLEX exists as a value of column STEPNO (usually in another row) in the same table?（）

• A、Define a UNIQUE constraint on the columns NEXT_STEPNO and STEPNO.
• B、Define a CHECK constraint on the NEXT_STEPNO column (NEXT_STEPNO = STEPNO).
• C、Define column STEPNO as the primary key of TABLEX and column NEXT_STEPNO as a foreign key referencing column STEPNO of the same table.
• D、Define column NEXT_STEPNO as the primary key of TABLEX and column STEPNO as a foreign key referencing column NEXT_STEPNO in the same table.

第3题：

When defining a referential constraint between the parent table T2 and the dependent table T1, which of the following is true?（）

• A、The list of column names in the FOREIGN KEY clause can be a subset of the list of column names in the primary key of T2 or a UNIQUE constraint that exists on T2.
• B、The list of column names in the FOREIGN KEY clause can be a subset of the list of column names in the primary key of T1 or a UNIQUE constraint that exists on T1.
• C、The list of column names in the FOREIGN KEY clause must be identical to the list of column names in the primary key of T2 or a UNIQUE constraint that exists on T2.
• D、The list of column names in the FOREIGN KEY clause must be identical to the list of column names in the primary key of T1 or a UNIQUE constraint that exists on T1.

第4题：

Which two statements are true about constraints? （）

• A、The UNIQUE constraint does not permit a null value for the column.
• B、A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.
• C、The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.
• D、The NOT NULL constraint ensures that null values are not permitted for the column.

第5题：

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);

第6题：

Which constraint can be defines only at the column level?（）

• A、UNIQUE
• B、NOT NULL
• C、CHECK
• D、PRIMARY KEY
• E、FOREIGN KEY

第7题：

Which constraint can be defined only at the column level? （）

• A、UNIQUE
• B、NOT NULL
• C、CHECK
• D、PRIMARY KEY
• E、FOREIGN KEY

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第13题：

Which of the following constraint types can be used to ensure the value of an INTEGER column references only positive values?（）

• A、Unique
• B、Check
• C、Referential
• D、Informational

第14题：

What type of constraint is used to ensure that each row inserted into the EMPLOYEE table with a value in the WORKDEPT column has a row with a corresponding value in the DEPTNO column of the DEPARTMENT table?（）

• A、A check constraint on the EMPLOYEE table
• B、A unique constraint on the EMPLOYEE table WORKDEPT column
• C、A foreign key reference from the DEPARTMENT tables DEPTNO column to the WORKDEPT column of the EMPLOYEE table
• D、A foreign key reference from the EMPLOYEE tables WORKDEPT column to the DEPTNO column of the DEPARTMENT table

第15题：

Which two statements are true about the primary key constraint in a table？ （）

• A、It is not possible to disable the primary key constraint.
• B、It is possible to have more than one primary key constraint in a single table.
• C、The primary key constraint can be referred by only one foreign key constraint.
• D、The primary key constraint can be imposed by combining more than one column.
• E、The non-deferrable primary key constraint creates an unique index on the primary key column if it is not already indexed.

第16题：

Which SQL statement defines the FOREIGN KEY constraint on the DEPTNO column of the EMP table?（）

• A、CREATE TABLE EMP (empno NUMBER(4), ename VARCNAR2(35), deptno NUMBER(7,2) NOT NULL CONSTRAINT emp_deptno_fk FOREIGN KEY deptno REFERENCES dept deptno);
• B、CREATE TABLE EMP (empno NUMBER(4), ename VARCNAR2(35), deptno NUMBER(7,2) CONSTRAINT emp_deptno_fk REFERENCES dept (deptno));
• C、CREATE TABLE EMP (empno NUMBER(4) ename VARCHAR2(35), deptno NUMBER(7,2) NOT NULL, CONSTRAINT emp_deptno_fk REFERENCES dept (deptno) FOREIGN KEY (deptno));
• D、CREATE TABLE EMP (empno NUMBER(4), ename VARCNAR2(35), deptno NUMBER(7,2) FOREIGN KEY CONSTRAINT emp deptno fk REFERENCES dept (deptno));

第17题：

Examine the following command: CREATE TABLE (prod_id number(4), Prod_name varchar2 (20), Category_id number(30), Quantity_on_hand number (3) INVISIBLE); Which three statements are true about using an invisible column in the PRODUCTS table?（）

• A、The %ROWTYPE attribute declarations in PL/SQL to access a row will not display the invisible column in the output.
• B、The DESCRIBE commands in SQL *Plus will not display the invisible column in the output.
• C、Referential integrity constraint cannot be set on the invisible column.
• D、The invisible column cannot be made visible and can only be marked as unused.
• E、A primary key constraint can be added on the invisible column.

第18题：

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);

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