SQL Questions

Karan Bhardwaj

Score: 🔥 123

Beginner

Took 2 months

Programming Language

SQL

90%

Questions Attempted

20 / 20

Correct Answers

Incorrect Answers

Points Earned

🔥 18

Question 1

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 2

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 3

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 4

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 5

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 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

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 8

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 9

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 10

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 11

What is the key difference between the IN and EXISTS operators when used with subqueries?

IN checks for existence in a list, while EXISTS checks for existence in a table.
IN is used for single values, while EXISTS is used for multiple values.
IN compares values, while EXISTS checks for the presence of rows.
There is no difference; they are interchangeable.

Explanation:

IN compares a value against a list of values returned by a subquery. EXISTS checks whether the subquery returns any rows at all, regardless of the values.

Question 12

What is the purpose of the 'LIMIT' clause in SQL?

It filters rows based on a condition.
It sorts the result set.
It restricts the number of rows returned by the query.
It groups rows with the same values.

Explanation:

LIMIT is used to control how many rows are included in the query result, helping manage the amount of data returned.

Question 13

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 14

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 15

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 16

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

Explanation:

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

Question 17

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 18

To modify existing data in a table, which SQL statement would you use?

MODIFY
UPDATE
CHANGE
ALTER

Explanation:

The UPDATE statement in SQL allows you to change the values in existing rows of a table based on your criteria.

Question 19

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 20

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.