DAC DAC Database & SQL Analytics

Question 1

Which SQL clause is used to filter rows after aggregation has been performed?

Accepted Answer

HAVING

Answer

WHERE

Answer

GROUP BY

Answer

ORDER BY

Question 2

What is the difference between an INNER JOIN and a LEFT JOIN in SQL?

Accepted Answer

INNER JOIN returns only matching rows; LEFT JOIN returns all rows from the left table plus matching rows from the right

Answer

INNER JOIN returns all rows from both tables; LEFT JOIN returns only matching rows

Answer

LEFT JOIN always returns fewer rows than INNER JOIN

Answer

There is no functional difference between the two

Question 3

Which SQL aggregate function returns the number of non-NULL values in a column?

Accepted Answer

COUNT()

Answer

SUM()

Answer

MAX()

Answer

AVG()

Question 4

What does a database index primarily improve?

Accepted Answer

Data query and retrieval speed

Answer

Data insertion speed

Answer

Data storage compression

Answer

Data encryption overhead

Question 5

In SQL, what does the DISTINCT keyword do?

Accepted Answer

Removes duplicate values from the result set

Answer

Sorts results in ascending order

Answer

Filters rows based on a condition

Answer

Joins two tables together

Question 6

What is a primary key in a relational database?

Accepted Answer

A column or combination of columns that uniquely identifies each row in a table

Answer

A key used for encrypting sensitive data

Answer

The first column in every table by convention

Answer

A foreign key that references another table