Querying Databases with SQL
Learn to ask questions of relational databases and extract the exact answers you need. Master data filtering, multi-table joins, aggregation, and conditional logic with clear, practical SQL queries.
Like Duolingo, but for Querying Databases with SQL. Tomo turns the whole topic into a game you play five minutes a day, until it actually sticks.
27 levels across 4 sections, about 54 minutes end to end, roughly 11 days at five minutes a day. It moves through Retrieving and Filtering Data, Summarizing and Segmenting Numbers, Connecting Tables Across Relationships, and Writing Robust and Multi-Step Queries. It starts from scratch.
Free forever · No credit card · iPhone & Android
Key ideas in Querying Databases with SQL
- In a relational database, each horizontal row represents one complete individual record
- Each vertical column represents a specific attribute or property shared by those records
- A named table organizes rows and columns belonging to the same entity type
- SQL is a declarative language, meaning you state what data you want rather than how to get it
- The database engine decides under the hood how to search, loop, or fetch records efficiently without manual loops
- A basic SQL query begins with SELECT followed by the specific columns you want to view
- The FROM clause specifies the table that holds those columns
- SQL clauses follow a strict grammatical order where SELECT comes before FROM
- ORDER BY sorts output in ascending (ASC, default) or descending (DESC) order
- ORDER BY affects only the presentation of the query results; it never permanently rearranges stored data in the database
- Tables have no guaranteed natural order unless an explicit ORDER BY clause is used in the query
- The LIMIT clause caps the maximum number of rows returned by a query
- Using LIMIT lets you quickly inspect column names and sample data without loading millions of rows into memory
- A WHERE clause acts like a gatekeeper that tests every row independently against a condition
- If a row's condition turns out false (or unknown due to missing data), SQL leaves that row out of the results
- SQL uses standard comparison symbols like =, !=, <, and >= for filtering
You've tried the other tabs
Thirty open tabs. Four facts you actually kept.
You watched. You nodded. By Sunday it was gone.
One answer, then back to scrolling.
Eight weeks. You meant to finish. You didn't.
Tomo gives Querying Databases with SQL the Duolingo treatment: levels, streaks, and quick quizzes that test what you just learned. That game loop is what the tabs above never had, so it's the one you actually finish.
Here's what playing it feels like
A real question from this course. Take your best guess.
If you look straight down a vertical column in a database table, what are you looking at?
Get it right to open this lesson and 26 more in the app.
Where Querying Databases with SQL takes you
- 1
Retrieving and Filtering Data
- Extracting and Sorting What You Need
- Filtering Rows by Precise Conditions
- 2
Summarizing and Segmenting Numbers
- Aggregating Data into Summaries
- Segmenting Totals with Groups
- 3
Connecting Tables Across Relationships
- Linking Tables Through Shared Keys
- Preserving Missing Matches with Outer Joins
- 4
Writing Robust and Multi-Step Queries
- Handling Missing Values and Custom Logic
- Composing Queries with Subqueries and CTEs
4 sections · 8 units · 27 levels. Built to play, not to enroll.
Tomo is in ChatGPT
Tomo is also a ChatGPT plugin: the same playable courses, built and played inside your chat.
Add Tomo to ChatGPT- What to ask
- “Make me a Tomo course on black holes.” “Turn this chat into a Tomo course.”
- What you get
- Quick questions with instant feedback, hearts and stars, ready to play in about a minute.
- Where it goes
- No sign-up to start. Connect your Tomo account and your streak carries on in the app.
You pick the voice
Querying Databases with SQL is taught in the Bestie style: your friend who just gets it. Want a different feel? In the app you can spin up the same topic in any of Tomo's teaching styles. Same facts, totally different vibe.
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Start Querying Databases with SQL today.
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