From all the givens, don't understand why B is the correct answer. There is no prior index on the table according to the exhibit. Please explain. Thanks
View the Exhibit and examine the structure of the EMP table.
You executed the following command to add a primary key to the EMP table:
ALTER TABLE emp ADD CONSTRAINT emp_id_pk
PRIMARY KEY (emp_id) USING INDEX emp_id_idx;
Which statement is true regarding the effect of the command?
Name Null? Type
A. The PRIMARY KEY is created along with a new index.
B. The PRIMARY KEY is created and it would use an existing unique index.
C. The PRIMARY KEY would be created in a disabled state because it is using an existing index.
D. The statement produces an error because the USING clause is permitted only in the CREATE TABLE command.