Quiz Discussion

In an employee table to include the attributes whose value always have some value which of the following constraint must be used?

• 1]

  Null

• 2]

  Not null

• 3]

  Unique

• 4]

  Distinct

A _____ indicates an absent value that may exist but be unknown or that may not exist at all.

• 1]

  Empty tuple

• 2]

  New value

• 3]

  Null value

• 4]

  Old value

The primary key must be

• 1]

  Unique

• 2]

  Not null

• 3]

  Both Unique and Not null

• 4]

  Either Unique or Not null

CREATE TABLE employee (id INTEGER,name VARCHAR(20),salary NOT NULL);
INSERT INTO employee VALUES (1005,Rach,0);
INSERT INTO employee VALUES (1007,Ross, );
INSERT INTO employee VALUES (1002,Joey,335);

Some of these insert statements will produce an error. Identify the statement.

• 1]

  Insert into employee values (1005,Rach,0)

• 2]

  Insert into employee values (1002,Joey,335);

• 3]

  Insert into employee values (1007,Ross, );

• 4]

  None of the mentioned

If the attribute phone number is included in the relation all the values need not be entered into the phone number column. This type of entry is given as

• 1]

  0

• 2]

  -

• 3]

  Null

• 4]

  Empty space

SELECT name
FROM instructor
WHERE salary IS NOT NULL;

Selects

• 1]

  Tuples with null value

• 2]

  Tuples with no null values

• 3]

  Tuples with any salary

• 4]

  All of the mentioned

The result of _____unknown is unknown.

• 1]

  Xor

• 2]

  Or

• 3]

  And

• 4]

  Not

The predicate in a where clause can involve Boolean operations such as and. The result of true and unknown is_______ false and unknown is _____ while unknown and unknown is _____

• 1]

  Unknown, unknown, false

• 2]

  True, false, unknown

• 3]

  True, unknown, unknown

• 4]

  Unknown, false, unknown

Using the ______ clause retains only one copy of such identical tuples.

• 1]

  Null

• 2]

  Unique

• 3]

  Not null

• 4]

  Distinct