ROLLUP 

The ROLLUP operator in MySQL is used with the GROUP BY clause. It is used to create subtotals and grand totals in the result set.

The ROLLUP operator generates a result set that is similar to the one generated by the GROUP BY clause, but with additional rows that represent subtotals and grand totals. The added rows are generated by successively reducing the GROUP BY clause one column at a time, creating subtotals at each step. This can be very useful for generating reports that contain subtotals and totals. The syntax for the use of the ROLLUP is thus:

SELECT 
  column1, column2,...
FROM 
  table_name
GROUP BY
  column1, 
  column2, 
  column2 WITH ROLLUP

The GROUP BY clause in SQL is used to group rows that have the same values in specified columns into aggregated data. The WITH ROLLUP option is used to create subtotals and grand totals within the grouped result set.P

1. SELECT column1, column2,...: This part of the query is selecting the columns that you want to include in your result set.
2. FROM table_name: This part of the query specifies the table from which to retrieve the data.
3. GROUP BY column1, column2, column3 WITH ROLLUP: This part of the query groups the selected columns, creating a separate row for each group of unique values.
4. The WITH ROLLUP modifier causes MySQL to include extra rows that represent the subtotals (which are produced by grouping on column1 and column2, and column1, column2 and column3) and the grand total (which is produced by grouping on all of the selected columns).

Note: The order of columns in the GROUP BY clause matters when using WITH ROLLUP. The subtotals and grand totals are generated from right to left.