SQL Quiz: Test Your SQL Skills

This SQL quiz has 10 questions across the five topics data analysts use most, ordered from basics to advanced. Half are multiple choice. The other half are “write the query” tasks: you get a table and a goal, then pick the query that returns the right result.

Every question uses two small tables, customers and orders, and standard SQL that works the same way in PostgreSQL, MySQL, SQL Server, and SQLite. When you finish, you’ll see your score, your level, a breakdown by topic, and an explanation for every answer, including the ones you got right.

Here are three practice questions in the same style as the quiz, with answers. They aren’t in the test itself, so trying them won’t spoil your score.

1. Why does this query fail in most databases?

SELECT amount * 0.9 AS discounted
FROM orders
WHERE discounted > 100;

Answer: WHERE runs before SELECT, so the alias discounted doesn’t exist yet when rows are filtered. Repeat the expression instead: WHERE amount * 0.9 > 100. The same order of steps (FROM, WHERE, GROUP BY, HAVING, SELECT, ORDER BY) is why ORDER BY can use an alias and WHERE can’t.

2. What’s the difference between COUNT(*) and COUNT(email)?

Answer: COUNT(*) counts every row. COUNT(email) counts only the rows where email isn’t NULL, so on a table with missing emails, the two numbers differ. That gap is a quick way to check how complete a column is.

3. Write the query: label each order “large” if the amount is 100 or more, and “small” if it’s less.

orders (order_id, customer_id, order_date, amount)

Answer: Use CASE, SQL’s version of if-then-else. It checks each condition in order and returns the first match, and ELSE covers every other row:

SELECT order_id, amount,
  CASE
    WHEN amount >= 100 THEN 'large'
    ELSE 'small'
  END AS order_size
FROM orders;

SQL is one of the most used languages in tech: 59% of developers in Stack Overflow’s 2025 Developer Survey said they use it. For data analysts, it’s the everyday tool for pulling, cleaning, and summarizing data. Here’s what each quiz level lets you do on the job:

1. 1

   Beginner (0–3 correct)

   You can read simple queries. The next skill is pulling a filtered list from one table, like this week’s orders over $100 or every customer in one state, which is often the first request an analyst gets.

2. 2

   Basic (4–6 correct)

   You can combine tables and build simple summaries: orders per customer, revenue by product, sign-ups by week. That covers the recurring reports and one-off data pulls in many entry-level analyst jobs.

3. 3

   Intermediate (7–8 correct)

   You can answer layered business questions, like which customers stopped buying or which products beat the average, and prepare clean tables for dashboards in Power BI or Tableau.

4. 4

   Advanced (9–10 correct)

   You can build rankings, running totals, retention reports, and month-over-month changes in a single query. Window functions like these often come up in data analyst interviews.

The quickest way to move up a level is to write queries against tables every day. If you scored in the beginner or basic range, start with TripleTen’s free SQL course: 20 hours of short lessons with coding practice, covering grouping and sorting, table joins, and subqueries and CTEs.

If you scored intermediate or advanced, SQL is ready to be part of a bigger skill set. The Data Analytics program adds Python, Power BI, and predictive analytics, and you’ll build a portfolio of projects for data analyst jobs.