easy

Querying Data

SELECT, WHERE, ORDER BY, and GROUP BY — ask questions of a relational database, live.

SQL (Structured Query Language) is how you talk to a relational database. Data lives in tables — rows and named columns — and you describe what you want, not how to fetch it. The database figures out the rest.

This is a real SQLite database running entirely in your browser. Edit the query and run it. Changes you make with INSERT/UPDATE stick until you press Reset data.

schema:departments(id, name)employees(id, name, dept_id, salary, hire_year)

loading SQL engine…

The shape of a query

SELECT columns
FROM table
WHERE condition
ORDER BY column [ASC|DESC]
LIMIT n;

SELECT picks the columns (or * for all).
FROM names the table.
WHERE keeps only the rows matching a condition.
ORDER BY sorts the result; LIMIT caps how many rows come back.

Try: SELECT name, salary FROM employees WHERE salary > 100000 ORDER BY salary DESC;

Aggregating with GROUP BY

Aggregate functions collapse many rows into one value: COUNT, SUM, AVG, MIN, MAX. GROUP BY runs them per group rather than over the whole table:

SELECT dept_id, COUNT(*) AS headcount, AVG(salary) AS avg_salary
FROM employees
GROUP BY dept_id;

Use HAVING to filter groups (after aggregation), the way WHERE filters rows.

Takeaways

SQL is declarative — you state the result you want, not the steps.
SELECT … FROM … WHERE … ORDER BY covers a huge share of everyday queries.
GROUP BY plus an aggregate turns rows into per-group summaries.