Databases

Question 1

HAVING

Answer 1

Can be used on a select statement to specify a certain property you’re expecting in your result set.

Question 2

count(*)

Answer 2

A function that counts number of records. May be used as an aggregate function.

Question 3

What is the difference between implicit and explicit join.

Answer 3

The explicit joins utilizes the ON statement instead of the WHERE clause.

Question 4

What is the difference between normalized and denormalized databases.

Answer 4

Normalized databases are designed to minimize redundancy. Denormalized databases are designed to optimize read time.

i.e. a normalized database table will contain a foreign key, but looking up foreign data will require an expensive join.

In a denormalized database, data may exist redundantly across multiple tables.

Question 5

Aggregate function MAX()

Answer 5

Returns the maximum value from an aggregate.

Question 6

Aggregate function MIN()

Answer 6

Returns the minimum value from an aggregate.

Question 7

Aggregate function AVG()

Answer 7

Returns the average of the argument.

Question 8

COUNT()

Answer 8

Returns count of rows returned.

Question 9

COUNT(DISTINCT)

Answer 9

Returns count of a number of different values.

Question 10

SUM()

Answer 10

Returns sum of the arguments.