Quiz Discussion

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

You attempt to query the database with this command:

 SELECT nvl (100 / quantity, NONE)
 FROM inventory;

Why does this statement cause an error when QUANTITY values are null?

• 1]

  The expression attempts to divide by a null value

• 2]

  The data types in the conversion function are incompatible

• 3]

  The character string none should be enclosed in single quotes (‘ ‘)

• 4]

  A null value used in an expression cannot be converted to an actual value

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

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

The result of _____unknown is unknown.

• 1]

  Xor

• 2]

  Or

• 3]

  And

• 4]

  Not