The ROLLUP command in SQL is used to generate subtotals for multiple levels of aggregation in a single query. It allows you to compute summary statistics for a set of groups and subgroups, as well as the grand total of all groups combined, in a single SQL statement.

The ROLLUP command generates multiple levels of aggregation by creating additional rows that represent the subtotals for each level of grouping. These subtotals are then included in the final output of the query.

For example, let’s say you have a table that contains sales data for a company with columns for region, department, and sales amount. You could use the ROLLUP command to generate a summary report that shows the sales totals for each region, department, and the overall company sales total:

SELECT region, department, SUM(sales_amount) AS total_sales
FROM sales_data
GROUP BY ROLLUP(region, department)

This query would generate output that includes subtotals for each region, department, and the grand total for all regions and departments combined.

The ROLLUP command can also be used with multiple columns, allowing you to generate subtotals for multiple levels of aggregation. Additionally, it can be used in conjunction with other SQL functions, such as COUNT and AVG, to compute summary statistics for the subtotals and grand total.