W1 – SQL Basics Quiz

Your manager, Adwoa, is explaining the database structure. She points to the "customer_id" column in the customers table and says, "This column is special because it uniquely identifies every single customer. No two customers can have the same one." What is this type of column called?

• Foreign Key

• Unique Column

• Primary Key

• Index Column

In the database hierarchy, a Table (like customers) exists inside a ________, which in turn exists inside a Database.

• Column

• Schema

• Server

• Row

Adwoa gives you an Entity-Relationship Diagram (ERD) for a database. What is the primary purpose of this diagram for you as an analyst?

• To see the actual data inside the tables.

• To understand the tables, their columns, and how they are related to each other.

• To check the performance of SQL queries.

• To create new customer accounts.

To sort the results of a query from the highest value to the lowest value (e.g., most expensive to least expensive), you would use the ORDER BY clause followed by the keyword ____.

• ASC

• HIGH

• DESC

• LOW

Kofi from Marketing asks for "a list of all customers who live in Kumasi AND registered after January 1st, 2024." Which WHERE clause correctly represents this request?

• WHERE city = 'Kumasi' OR registration_date > '2024-01-01'

• WHERE city = 'Kumasi' AND registration_date < '2024-01-01'

• WHERE city = 'Kumasi' AND registration_date > '2024-01-01'

• WHERE city = 'Kumasi' OR registration_date < '2024-01-01'

A colleague shows you this query: SELECT * FROM products WHERE price > 50 AND < 100;. It's not working. What is the correct way to write this condition?

• WHERE price > 50 AND price < 100

• WHERE price IS BETWEEN 50 TO 100

• WHERE price > 50 OR < 100

• WHERE price IN (50, 100)

You've written a complex query for a team report. What is a crucial "soft skill" action you should take before sharing it with your colleagues?

• Add comments (--) to the SQL code to explain what each part of the query does.

• Don't share the query, just the final results.

• Name all your columns with short, one-letter aliases to save space.

• Make sure to use as many subqueries as possible to show your skill.

You find a bug in a query that powers a dashboard: it's double-counting sales. You've been asked to fix it. What is the most professional sequence of actions?

1. 1. Write and test a new, corrected query.

2. 2. Communicate to the stakeholders that you have identified the issue and are working on a fix.

3. 3. Deploy the fix and verify that the dashboard now shows the correct numbers.

4. 4. Understand why the original query was wrong.

• 2, 4, 1, 3

• 4, 1, 3, 2

• 3, 2, 4, 1

• 1, 2, 4, 3

You receive a new business request from the sales team. Put your analytical steps in the most logical order for a professional workflow.

1. 1. Write the final SQL query in your editor.

2. 2. Understand the business question being asked.

3. 3. Explore the relevant tables with LIMIT to see the column names and data types.

4. 4. Verify your results to ensure they make sense.

• 2, 3, 4, 1

• 1, 2, 3, 4

• 4, 2, 3, 1

• 2, 3, 1, 4

Your colleague is new to SQL and asks for the correct order of clauses in a basic query. Arrange these fundamental SQL clauses in the order they must be written.

1. 1. WHERE

2. 2. SELECT

3. 3. LIMIT

4. 4. FROM

5. 5. ORDER BY

• 3, 2, 4, 1, 5

• 2, 4, 1, 5, 3

• 2, 4, 5, 3, 1

• 4, 2, 1, 5, 3