SQL Questions

Kajal Saini

Score: 🔥 44

Beginner

Took 2 months

Programming Language

SQL

80%

Questions Attempted

15 / 15

Correct Answers

Incorrect Answers

Points Earned

🔥 12

Question 1

What SQL clause is used to filter rows in a result set based on specific conditions?

SELECT
WHERE
FROM
ORDER BY

Explanation:

The WHERE clause is used to specify conditions that rows must meet to be included in the query results.

Question 2

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 3

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 4

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 5

You want to select the department with the highest average salary. What SQL clause would you use to filter the grouped results based on the calculated average salary?

WHERE
HAVING
ORDER BY
LIMIT

Explanation:

HAVING is used to filter groups after the GROUP BY clause, making it suitable for conditions involving aggregate functions like AVG used for calculating the average salary.

Question 6

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 7

Which keyword is used in conjunction with the UPDATE statement to specify the conditions for updating rows?

WHEN
IF
WHERE
CONDITION

Explanation:

The WHERE clause is crucial with UPDATE as it defines which rows should be modified. Without it, all rows would be updated.

Question 8

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 9

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

Explanation:

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

Question 10

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 11

What does the asterisk (*) symbol represent when used in a SELECT statement?

A specific column name
All columns
A wildcard for searching data
A comment indicator

Explanation:

In SQL, the asterisk (*) is a shorthand to select all columns from a table when used in the SELECT clause.

Question 12

What is the purpose of the COUNT() function in SQL?

Returns the number of rows in a table
Calculates the sum of values in a column
Returns the average value of a column
Finds the minimum value in a column

Explanation:

COUNT() is an aggregate function used to count the number of rows in a table or the number of rows that meet a specific condition in a query.

Question 13

What potential issue should be considered when using correlated subqueries?

They can lead to performance issues if not used carefully.
They cannot be used with aggregate functions.
They require the use of the JOIN clause.
They cannot return more than one column.

Explanation:

Correlated subqueries execute for each row of the outer query, potentially leading to performance bottlenecks, especially with large datasets. Proper indexing and optimization are crucial.

Question 14

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.

Question 15

What does SQL stand for?

Structured Query Language
Simple Query Language
Standard Query Logic
System Query Language

Explanation:

SQL stands for Structured Query Language. It's a standardized language for managing and interacting with relational databases.