Advanced SQL Questions

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11.

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

A

Null

B

Not null

C

Unique

D

Distinct

Correct Answer: B

None.

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12.

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

A

Null

B

Unique

C

Not null

D

Distinct

Correct Answer: D

None.

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13.

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

A

Insert into employee values

B

Insert into employee values

C

Insert into employee values

D

None of the mentioned

Correct Answer: C

None.

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14.

The primary key must be

A

Unique

B

Not null

C

Both Unique and Not null

D

Either Unique or Not null

Correct Answer: C

None.

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15.

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

A

The expression attempts to divide by a null value

B

The data types in the conversion function are incompatible

C

The character string none should be enclosed in single quotes

D

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

Correct Answer: A

None.

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16.

The result of _____unknown is unknown.

A

Xor

B

Or

C

And

D

Not

Correct Answer: D

None.

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17.

Aggregate functions are functions that take a ___________ as input and return a single value.

A

Collection of values

B

Single value

C

Aggregate value

D

Both Collection of values & Single value

Correct Answer: A

None.

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18.

Which of the following should be used to find the mean of the salary ?

A

Mean

B

Avg

C

Sum

D

Count

Correct Answer: B

None.

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19.

If we do want to eliminate duplicates, we use the keyword ______in the aggregate expression.

A

Distinct

B

Count

C

Avg

D

Primary key

Correct Answer: A

None.

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20.

All aggregate functions except _____ ignore null values in their input collection.

A

Count

B

Count

C

Avg

D

Sum

Correct Answer: B

None.

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