Скачать или смотреть Understanding ROLLUP and CUBE functions in SQL

In SQL, the ROLLUP and CUBE operators are used to generate subtotals and grand totals for a set of columns in the result set. These operators are typically used in conjunction with the GROUP BY clause to create summary reports with hierarchical aggregations.

ROLLUP:

The ROLLUP operator is used to create subtotals for a specified list of columns in the GROUP BY clause, and it also generates grand totals.
The result set produced by ROLLUP includes rows with subtotals and a grand total, and each subtotal level represents a grouping based on the specified columns.

Example:

SELECT department, employee, SUM(salary)
FROM employee_table
GROUP BY ROLLUP (department, employee);

CUBE:

The CUBE operator is similar to ROLLUP but generates all possible combinations of subtotals for the specified columns. This includes subtotals for individual columns, pairs of columns, and so on.
The result set produced by CUBE is more extensive than that of ROLLUP, as it considers all possible combinations of the specified columns.
Syntax:

SELECT department, employee, SUM(salary)
FROM employee_table
GROUP BY CUBE (department, employee);

In summary, both ROLLUP and CUBE are useful for creating summary reports with aggregated data. ROLLUP generates subtotals and a grand total based on a specified hierarchy, while CUBE generates all possible combinations of subtotals for the specified columns. Depending on your reporting needs, you can choose between ROLLUP and CUBE to generate the desired level of summarization in your result set.


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