The EMP table exists in your schema. You want to execute the following query:SELECT ename,

e the query as shown in the Exhibit to retrieve all versions of the row that exist between two SCNs.View the Exhibit.Which two statements about the results of the query shown in the Exhibit are correct？ （）(Choose two.)

A. The LAST_SCN value in the first row is NULL, which means that the versions of the row still exist at SCN 6636300.

B. The LAST_SCN value in the second row in NULL, which means that the version of the row still exists at SCN 6636300.

C. The LAST_SCN value in the third row is 6636280, which means that the version of row exists above SCN 6636280.

D. The LAST_SCN value in the second row is NULL, which means that the version of the row no longer exists because it was deleted.

meric identifier automatically assigned when a row is added, has an EDLEVEL column that permits only the values ‘C‘, ‘H‘ and ‘N‘, and permits inserts only when a corresponding value for the employee‘s department exists in the DEPARTMENT table.Which of the following CREATE statements will successfully create this table？（）

A.CREATE TABLE emp (empno SMALLINT NEXTVAL GENERATED ALWAYS AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3) NOT NULL, edlevel CHAR(1), PRIMARY KEY emp_pk (empno), FOREIGN KEY emp_workdept_fk ON (workdept) REFERENCES department (deptno), CHECK edlevel_ck VALUES (edlevel IN (‘C‘,‘H‘,‘N‘)), );

B.CREATE TABLE emp (empno SMALLINT NOT NULL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3), edlevel CHAR(1), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY (workdept) REFERENCES department (deptno), CONSTRAINT edlevel_ck CHECK edlevel VALUES (‘C‘,‘H‘,‘N‘) );

C.CREATE TABLE emp (empno SMALLINT NEXTVAL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3) NOT NULL, edlevel CHAR(1) CHECK IN (‘C‘,‘H‘,‘N‘)), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY department (deptno) REFERENCES (workdept) );

D.CREATE TABLE emp (empno SMALLINT NOT NULL GENERATED BY DEFAULT AS IDENTITY, firstname VARCHAR(30) NOT NULL, lastname VARCHAR(30) NOT NULL, workdept CHAR(3), edlevel CHAR(1), CONSTRAINT emp_pk PRIMARY KEY (empno), CONSTRAINT emp_workdept_fk FOREIGN KEY (workdept) REFERENCES department (deptno), CONSTRAINT edlevel_ck CHECK (edlevel IN (‘C‘,‘H‘,‘N‘)) );

以下语句错误的是()

A. alter table emp delete column addcolumn;

B. alter table emp modify column addcolumn char(10);

C.alter table emp change addcolumn addcolumn int;

D. alter table emp add column addcolumn int;

以下能够删除一列的是()

A.alter table emp remove addcolumn

B.alter table emp drop column addcolumn

C.alter table emp delete column addcolumn

D.alter table emp delete addcolumn

A.DELETE * FROM　EMP

B.DELETE FROM　EMP

C.TRUNCATE TABLE　EMP

D.DELETE TABLE　EMP

A.DELETE * FROM　EMP

B.DELETE FROM　EMP

C.TRUNCATE TABLE　EMP

D.DELETE TABLE　EMP

A.alter table emp drop column addcolumn

B.alter table emp remove addcolumn

C.alter table emp delete addcolumn

D.alter table emp delete column addcolumn