What does GROUP BY do in SQL?

What does GROUP BY do in SQL?

• A. Sorts rows by a specified column.
• B. Aggregates rows into groups based on specified columns.
• C. Joins rows from two tables.
• D. Filters rows based on a condition.

Answer: (B)

Grouping in SQL collects rows that share the same values in the specified columns into a single summary row for each distinct combination. When you use these columns in GROUP BY, the database forms a group for every unique set of values and then you run aggregate calculations (like COUNT, SUM, AVG, or MAX) within each group, producing one result row per group. This is different from sorting (which just reorders rows), joining (which combines rows from multiple tables), or filtering with a WHERE clause (which removes rows before grouping). You can also refine the results by using HAVING to filter groups after the aggregation.