What does the WHERE clause do in a SQL query?

Filters rows based on a condition

Limits the number of columns returned

easy #sql #select #beginners #filtering #sorting #where-clause

QUESTION 01 OF 10

SQL Basics: Writing Your First Queries

Get comfortable with the fundamental building blocks of SQL, including SELECT statements, filtering rows, and sorting results. This quiz is designed for absolute beginners taking their first steps with databases.

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Which SQL keyword is used to retrieve data from a table?

About this Quiz

This interactive assessment is designed to test your understanding of SQL Basics: Writing Your First Queries. Whether you are a beginner looking to grasp the basics or an experienced professional aiming to refine your skills, quizzes are an excellent way to validate your knowledge and identify areas for improvement.

Instructions

Read each question carefully before answering.
Some questions may have multiple correct answers.
There is no time limit, so take your time to think.
You will receive immediate feedback after submission.

Learning Outcomes

Self-assess your current skill level.
Reinforce key concepts through active recall.
Identify knowledge gaps to focus your study.
Gain confidence in your technical expertise.
Reinforce memory and recall.

Topic Overview

Questions in this quiz:

1. Which SQL keyword is used to retrieve data from a table?

GET
FETCH
SELECT
READ

Hint: SELECT is the SQL keyword used to query and retrieve data from one or more tables. It is the most commonly used SQL statement and forms the foundation of every read query.

2. Which query retrieves all columns from a table called <code>employees</code>?

Hint: The asterisk <code>*</code> is a wildcard that means all columns. <code>SELECT * FROM employees;</code> retrieves every column for every row in the table. While convenient, it's best practice in production to list only the columns you need.

3. What does the WHERE clause do in a SQL query?

Sorts the result set
Groups rows by a column value
Filters rows based on a condition
Limits the number of columns returned

Hint: The WHERE clause filters rows so that only those meeting the specified condition are included in the result. For example, <code>WHERE age > 30</code> returns only rows where the age column is greater than 30.

4. What will the following query return?

All employees younger than 30
All employees exactly 30 years old
The name and age of employees who are 30 or older
All columns for employees who are 30 or older

Hint: The query selects only the <code>name</code> and <code>age</code> columns and filters with <code>age >= 30</code>, which means greater than or equal to 30. Only those two columns are returned, not all columns.

5. In SQL, the ORDER BY clause sorts results in ascending order by default.

True
False

Hint: True. <code>ORDER BY column_name</code> sorts results in ascending (ASC) order by default — smallest to largest, or A to Z. To sort in descending order, you must explicitly add the <code>DESC</code> keyword.

6. Which keyword removes duplicate values from a query's result set?

UNIQUE
DISTINCT
FILTER
REMOVE DUPLICATES

Hint: DISTINCT eliminates duplicate rows from the result. For example, <code>SELECT DISTINCT city FROM customers;</code> returns each city name only once, even if many customers share the same city.

7. What is the correct order of these clauses in a SQL SELECT statement?

FROM → WHERE → SELECT → ORDER BY
SELECT → FROM → ORDER BY → WHERE
SELECT → FROM → WHERE → ORDER BY
WHERE → FROM → SELECT → ORDER BY

Hint: The standard clause order in a SQL query is: SELECT → FROM → WHERE → ORDER BY. While the database processes <code>FROM</code> and <code>WHERE</code> before <code>SELECT</code> internally, this is the correct syntax order you must write them in.

8. Which query returns only the first 5 rows from the <code>products</code> table?

Hint: <code>LIMIT 5</code> restricts the result to the first 5 rows. It is supported by most databases (MySQL, PostgreSQL, SQLite). SQL Server uses <code>TOP 5</code> and Oracle uses <code>FETCH FIRST 5 ROWS ONLY</code>, but <code>LIMIT</code> is the most widely known syntax.

9. You can use the <code>AND</code> and <code>OR</code> operators in a WHERE clause to combine multiple conditions.

True
False

Hint: True. <code>AND</code> requires all conditions to be true, while <code>OR</code> requires at least one condition to be true. You can combine them and use parentheses to control precedence, e.g., <code>WHERE age > 25 AND (city = 'NYC' OR city = 'LA')</code>.

10. What does the following query do?

Returns the 3 lowest-paid employees
Returns the name and salary of the 3 highest-paid employees
Returns all employees sorted by salary, showing only 3 columns
Returns employees whose salary rank is 3

Hint: <code>ORDER BY salary DESC</code> sorts employees from highest to lowest salary. <code>LIMIT 3</code> then keeps only the top 3 rows. Together, these two clauses form a common pattern for retrieving the top N records by a given value.