GROUP BY with ORDER BY in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the GROUP BY clause do in SQL?

It groups rows that have the same values in specified columns into summary rows, like grouping all sales by each product.

beginner

Why do we use ORDER BY after GROUP BY?

To sort the grouped results in a specific order, such as sorting groups by total sales from highest to lowest.

intermediate

Can you use aggregate functions like SUM() with GROUP BY? Give an example.

Yes. For example, SELECT product, SUM(sales) FROM sales_data GROUP BY product; sums sales for each product group.

intermediate

What happens if you use ORDER BY on a column not in the GROUP BY clause?

You can order by aggregate results or columns in the SELECT list, but not by columns not grouped or aggregated, or it causes an error.

beginner

Write a simple SQL query that groups sales by region and orders the result by total sales descending.

Example: SELECT region, SUM(sales) AS total_sales FROM sales_data GROUP BY region ORDER BY total_sales DESC;

What is the purpose of the GROUP BY clause in SQL?

A To delete duplicate rows

B To sort rows in ascending order

C To combine rows with the same values into groups

D To filter rows based on a condition

GROUP BY groups rows that share the same values in specified columns.

Which clause should come first in a SQL query: GROUP BY or ORDER BY?

A ORDER BY before GROUP BY

B GROUP BY before ORDER BY

C They can be in any order

D Only one of them can be used

GROUP BY must come before ORDER BY to group rows before sorting.

What will this query do? SELECT city, COUNT(*) FROM customers GROUP BY city ORDER BY COUNT(*) DESC;

A Group customers but not sort results

B Sort customers by city name

C Count total customers without grouping

D Count customers per city and sort cities by count descending

It groups customers by city, counts them, and orders cities by count descending.

Can you use ORDER BY on an aggregate function result like SUM(sales)?

A Yes, to sort groups by the aggregate value

B No, aggregate functions cannot be ordered

C Only if you use DISTINCT

D Only if you use HAVING

ORDER BY can sort results by aggregate function values.

If you group by department, which column can you order by?

A Only columns in GROUP BY or aggregates

B Any column in the table

C Only columns not in GROUP BY

D Only columns with unique values

You can order by grouped columns or aggregate results.

Explain how GROUP BY and ORDER BY work together in a SQL query.

Think about grouping first, then sorting the groups.

Write a SQL query that groups sales by product category and orders the categories by total sales ascending.

Use SUM() and ORDER BY with ASC.