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
题目
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.