Group By (CLAUSE)

Definition

GROUP BY is a SQL clause used to group rows that have the same values in specified columns into summary rows, often used with aggregate functions like COUNT(), SUM(), AVG(), MAX(), MIN().

What Problem It Solves

It solves the problem of data summarization by allowing aggregation of multiple rows into meaningful grouped results (e.g., total sales per customer).

What Happens If Not Used

You get raw row-level data, not grouped summaries. Aggregations will apply to the entire table instead of categories.

Easy Wording

It “collects similar data together” and then calculates results for each group.

Technical Example

A shop has many orders. GROUP BY customer shows total orders per customer instead of listing every order separately. SELECT department, COUNT(*) FROM employees GROUP BY department; Result: number of employees in each department.