SQL Lesson 2: COUNT, SUM and GROUP BY

SheetDrill SQL SQL Lesson 2 · COUNT, SUM and GROUP BY

SQL · Lesson 2

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SQL Lesson 2 done.

You can count, total and average, split the numbers by group, filter groups with HAVING and count unique values. That's the core of every report and dashboard query. Next up: combining tables.

SQL Lesson 3: JOINs →

What you're learning

COUNT(*) counts rows, SUM(col) adds a column up, AVG(col) averages it. On their own they turn the whole table into one row. GROUP BY region gives one row per region instead: SELECT region, SUM(revenue) FROM orders GROUP BY region.

WHERE filters rows before grouping; HAVING filters groups after, so it's where conditions on totals go: HAVING COUNT(*) >= 2. COUNT(DISTINCT customer) counts each customer once.