Which statement best describes the effect of GROUP BY when used with aggregate functions?

Which statement best describes the effect of GROUP BY when used with aggregate functions?

• A. It groups rows by the values of specified columns so aggregates apply per group.
• B. It sorts the result in ascending order.
• C. It filters groups before applying aggregates.
• D. It duplicates rows to create larger groups.

Answer: (A)

Grouping rows by the values of the specified columns to compute aggregates per group is what happens when you combine GROUP BY with aggregate functions. GROUP BY creates a separate group for each distinct combination of values in the listed columns, and the aggregate functions (like SUM, AVG, COUNT) are then calculated within each group, giving one result row per group. For example, grouping sales data by region yields a total for each region rather than a single overall total. This differs from sorting, which reorganizes the order of rows and is done with ORDER BY. It also isn’t about filtering; WHERE can limit rows before grouping, and HAVING can filter groups after aggregation. And it doesn’t duplicate rows to form larger groups—GROUP BY partitions rows into groups based on the unique values in the specified columns.

Grouping rows by the values of the specified columns to compute aggregates per group is what happens when you combine GROUP BY with aggregate functions. GROUP BY creates a separate group for each distinct combination of values in the listed columns, and the aggregate functions (like SUM, AVG, COUNT) are then calculated within each group, giving one result row per group. For example, grouping sales data by region yields a total for each region rather than a single overall total.

This differs from sorting, which reorganizes the order of rows and is done with ORDER BY. It also isn’t about filtering; WHERE can limit rows before grouping, and HAVING can filter groups after aggregation. And it doesn’t duplicate rows to form larger groups—GROUP BY partitions rows into groups based on the unique values in the specified columns.