SQL practice with real tables to explore and queries to write.

Follow a path, or find the concept you need

The SQL practice workspace has its own question path, separate from general coding. Begin at the first exercise, continue from your saved position or open the next unfinished problem. Search by question number, title, topic or level when you want focused revision.

The training database contains related tables such as customers, orders, order items, products and employees. Review the schema and sample rows before writing a query. Knowing which column identifies a customer and which table stores a transaction prevents many incorrect joins.

Reason about rows before you add more SQL

Consider a table of orders with a customer_id and an amount. To find customers whose total order value exceeds 1,000, first group rows by customer_id, then calculate SUM(amount), and use HAVING to filter those totals. WHERE filters individual rows before grouping; HAVING filters groups after aggregation.

Before joining another table, ask what one output row should represent. Joining orders to order items can create several rows for one order. If you sum an order total after that join, you may count it repeatedly. Defining the intended row level first makes the query easier to trust.

Check results against more than one dataset

Run sample checks the visible data and helps you inspect output and errors. Submit query checks the sample and hidden datasets, then saves the verdict. Both must pass for the exercise to count as complete. Hidden data can expose assumptions that happen to work on the sample, such as every customer having an order.

• Use the requested column order and include ORDER BY when row order is required.
• Consider duplicate values, missing matches and ties in rankings.
• Compare the returned rows with the question’s meaning, not only its example.

Understand the practice environment

Queries, view exercises and index exercises run in an isolated SQLite-based environment with selected MySQL-style helper functions. Designated account and permission exercises use a labelled simulation. This is a training workspace, rather than a complete MySQL server or access to a production database.

Your report distinguishes distinct completed exercises from check accuracy across submissions. Returning to the beginning preserves your completed results. Use the remaining-work view to choose a new task, and revisit incorrect submissions to learn why a seemingly reasonable query produced the wrong rows.