Multiple choice technology databases

WHat is not true about the constaints ?

  1. A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.

  2. The UNIQUE constraint does not permit a null value for the column

  3. The NOT NULL constraint ensures that null values are not permitted for the column

  4. The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Explanation

The UNIQUE constraint DOES permit null values (unlike PRIMARY KEY), and typically allows multiple nulls since null != null. PRIMARY KEY and FOREIGN KEY constraints do create unique indexes automatically. The NOT NULL statement about UNIQUE constraints is the correct falsehood among these.

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