【单选题】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);
【单选题】Given that the current directory is empty, and that the user has read and write privileges to the current, and the following: Which statement is true?()
A.
Compilation fails.
B.
Nothing is added to the file system.
C.
Only a new file is created on the file system.
D.
Only a new directory is created on the file system.
E.
Both a new file and a new directory are created on the file system.
【单选题】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);