How do I use GROUP BY on multiple columns in SQL?

Using GROUP BY on multiple columns in SQL allows you to group rows based on combinations of values in those columns. This is useful when you need to analyze data at a more granular level, considering multiple dimensions together.

General Syntax:

Key Points:

1. Columns in GROUP BY:
   • Include all the columns you want to group by.
   • The query groups rows that have the same values in all specified columns.
2. Aggregate Functions:
   • Use aggregate functions like COUNT(), SUM(), AVG(), etc., to compute summaries for each group.
3. Order of Columns:
   • The order of columns in the GROUP BY clause matters if you later use ORDER BY without specifying a custom order.

Example Use Case:

Imagine a table sales with the following columns: region, product, and revenue.

Query:

To find the total revenue for each combination of region and product:

How It Works:

• The query groups rows by unique combinations of region and product.
• For each group, it calculates the SUM(revenue).

Result:

Notes:

• All non-aggregate columns in the SELECT statement must be included in the GROUP BY clause.
• If you add more columns to the GROUP BY clause, it further subdivides the groups.

By combining multiple columns in GROUP BY, you can analyze data with more complex relationships.