SQL Questions

Diwakar Bhardwaj

Score: 🔥 51

Beginner

Took 2 months

Programming Language

SQL

80%

Questions Attempted

15 / 15

Correct Answers

Incorrect Answers

Points Earned

🔥 12

Question 1

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 2

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 3

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 4

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.

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

Which SQL statement is used to add new rows into a table?

ADD
INSERT
CREATE
APPEND

Explanation:

The INSERT statement is used to insert new rows with data into an existing table within a database.

Question 7

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 8

What is the difference between CURDATE() and NOW() in SQL?

CURDATE() returns the current date, NOW() returns the current time.
CURDATE() returns the current date, NOW() returns the current date and time.
CURDATE() returns the current date and time, NOW() returns the current date.
They are interchangeable.

Explanation:

CURDATE() returns only the current date in 'YYYY-MM-DD' format, while NOW() returns both the current date and time.

Question 9

How would you select the top 5 highest-scoring games from a table named 'games' with a column called 'score'?

SELECT * FROM games ORDER BY score DESC LIMIT 5;
SELECT * FROM games ORDER BY score ASC LIMIT 5;
SELECT TOP 5 * FROM games ORDER BY score DESC;
SELECT * FROM games WHERE score LIMIT 5;

Explanation:

This query sorts the games by score in descending order and then uses LIMIT to retrieve only the top 5.

Question 10

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 11

What type of join returns all rows from both tables, regardless of whether there is a match?

INNER JOIN
LEFT JOIN
RIGHT JOIN
FULL OUTER JOIN

Explanation:

A FULL OUTER JOIN returns all rows from both the left and right tables. If there are no matches on one side, it fills in NULL values for the corresponding columns.

Question 12

Which SQL function would you use to combine the first and last names from two different columns into a single column?

COMBINE()
MERGE()
CONCAT()
JOIN()

Explanation:

CONCAT() is a string function that takes two or more strings as arguments and concatenates them into a single string.

Question 13

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 14

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 15

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.