SQL Questions

Vikas Vimal (Vikki)

Score: 🔥 175

Beginner

Took 2 months

Programming Language

SQL

26%

Questions Attempted

15 / 15

Correct Answers

Incorrect Answers

Points Earned

🔥 4

Question 1

In a SQL query, what does the logical operator 'AND' do?

It combines two conditions, and both conditions must be true for the row to be included.
It combines two conditions, and at least one condition must be true for the row to be included.
It negates a condition.
It sorts the results in descending order.

Explanation:

The AND operator requires both conditions to be true for the combined condition to be true.

Question 2

In which scenario would a subquery be a more suitable choice than a JOIN operation?

When you need to combine data from multiple tables based on a common column.
When you need to filter data based on a condition that involves a separate query.
When you need to update data in one table based on data from another table.
When you need to sort data from multiple tables based on a common column.

Explanation:

Subqueries excel at providing dynamic filtering conditions for the main query. If the filtering relies on a separate query's results, using a subquery makes the logic clearer and more concise than attempting to achieve the same with JOINs.

Question 3

By default, how does the 'ORDER BY' clause sort data?

Randomly
Alphabetically
In ascending order
In descending order

Explanation:

If no specific order (ASC or DESC) is specified, ORDER BY defaults to sorting in ascending order.

Question 4

How would you convert the text 'hello world' to uppercase in SQL?

TO_UPPER('hello world')
UPPER('hello world')
UCASE('hello world')
MAKE_UPPER('hello world')

Explanation:

UPPER() is a string function that takes a string as an argument and returns the string converted to uppercase.

Question 5

What is the purpose of a subquery in SQL?

To modify data in multiple tables simultaneously.
To create a temporary table for intermediate results.
To retrieve data from a table that will be used in a larger query.
To define a new aggregate function.

Explanation:

A subquery is a query nested inside another query, used to fetch data that the main query then uses, effectively acting as a dynamic input for the main query.

Question 6

Which of the following is NOT a valid SQL data type?

INTEGER
VARCHAR
BOOLEAN
FLOAT

Explanation:

While some database systems have extensions or specific types for boolean values, standard SQL does not have a BOOLEAN data type.

Question 7

Which SQL statement is used to remove rows from a table?

REMOVE
DELETE
TRUNCATE
DROP

Explanation:

While both DELETE and TRUNCATE remove rows, DELETE is used to selectively remove rows based on a condition, while TRUNCATE removes all rows.

Question 8

Which data type would be most suitable for storing a person's last name in a SQL database?

INTEGER
DATE
VARCHAR
DECIMAL

Explanation:

VARCHAR (Variable Character) is used for storing strings of text, making it appropriate for a last name which can vary in length.

Question 9

How would you sort results in descending order by the 'date_created' column?

ORDER BY date_created DESC
ORDER BY date_created ASC
SORT BY date_created DESC
SORT BY date_created ASC

Explanation:

The 'DESC' keyword after the column name in the ORDER BY clause signals descending order sorting.

Question 10

What type of join returns all rows from the left table, even if there are no matching rows in the right table?

INNER JOIN
LEFT JOIN
RIGHT JOIN
FULL JOIN

Explanation:

A LEFT JOIN returns all rows from the left table (the table mentioned before LEFT JOIN) and the matching rows from the right table. If there are no matches, it fills in NULL values for the columns from the right table.

Question 11

You are using a subquery to fetch a list of product IDs from an 'Orders' table. What is the main purpose of using the DISTINCT keyword within this subquery?

To sort the product IDs in ascending order.
To limit the number of product IDs returned.
To retrieve only unique product IDs, eliminating duplicates.
To filter product IDs based on a specific condition.

Explanation:

The DISTINCT keyword ensures that the subquery's result set contains only unique values, removing any duplicate product IDs, which is essential for accurate comparisons or joins in the main query.

Question 12

Which comparison operator means 'not equal to' in SQL?

Explanation:

Both '!=' and '<>' are used for 'not equal to' in SQL. They are interchangeable.

Question 13

What is the primary clause used to retrieve data from a table in SQL?

RETRIEVE
FETCH
SELECT
GET

Explanation:

The SELECT clause is the core of retrieving data in SQL. It specifies the columns you want to get from a table.

Question 14

Which aggregate function would you use to find the highest value in a column?

SUM()
AVG()
MIN()
MAX()

Explanation:

MAX() is an aggregate function that returns the maximum value in a set of values (typically a column).

Question 15

What SQL clause is used to group rows with the same value in one or more columns into a summary row?

WHERE
ORDER BY
GROUP BY
SELECT

Explanation:

The GROUP BY clause is specifically designed to group rows based on identical values in specified columns, allowing for aggregate functions to be applied to each group.