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?

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  1. ALTER TABLE students ADD PRIMARY KEY student_id;

  2. ALTER TABLE students ADD CONSTRAINT PRIMARY KEY (student_id);

  3. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY student_id;

  4. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id);

  5. ALTER TABLE students MODIFY CONSTRAINT stud_id_pk PRIMARY KEY (student_id);

Show answer
Correct Option: D

AI Explanation

To add a primary key on the STUDENT_ID column in the STUDENTS table, you can use the following statement:

D. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id);

Explanation for each option:

A. ALTER TABLE students ADD PRIMARY KEY student_id; This option is incorrect because it is missing the CONSTRAINT keyword before PRIMARY KEY.

B. ALTER TABLE students ADD CONSTRAINT PRIMARY KEY (student_id); This option is incorrect because it is missing a name for the constraint. A constraint must have a unique name.

C. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY student_id; This option is incorrect because it is missing parentheses around the column name student_id.

D. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id); This option is correct because it uses the correct syntax to add a constraint with a name (stud_id_pk) on the column student_id as the primary key.

E. ALTER TABLE students MODIFY CONSTRAINT stud_id_pk PRIMARY KEY (student_id); This option is incorrect because MODIFY CONSTRAINT is used to modify an existing constraint, not to add a new constraint.

The correct answer is D. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id). This option is correct because it adds a primary key constraint with the name stud_id_pk on the column student_id in the STUDENTS table.

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