How to use rollup in sql

rollup is an aggregate function in SQL that is used to perform multi-level grouping and summary of data in a hierarchical structure. Its syntax is: rollup(expression). By aggregating data at different granularities, the rollup function can easily create multi-level aggregations, improve query performance, and allow users to explore data at different granularities.

Usage of rollup in SQL

What is rollup?

rollup is an aggregate function in SQL that is used to group and summarize data in a hierarchy. It allows users to perform multi-level aggregation of data, from the most detailed level to the most summary level.

How to use rollup?

The syntax of the rollup function is as follows:

rollup(expression)

Among them:

• expression: the expression to be grouped and aggregated, which can be a column name or an aggregate function or other calculations.

Usage example of rollup function:

Example 1: Summarize sales by "region" and "product" groups

SELECT region, product, SUM(sales)
FROM sales_table
GROUP BY ROLLUP(region, product);

This query will generate the following output:

##CentralProduct B1500CentralTotal2500##EastEastEastWestWestWestGrand Total

region	product	sum(sales)
Central	Product A	1000
Product A	500
Product B	750
Total	1250
Product A	700
Product B	900
Total	1600
	5350

Example 2: Summarize order quantities by time hierarchy grouping

<strong>SELECT year, quarter, month, COUNT(order_id)
FROM orders_table
GROUP BY ROLLUP(year, quarter, month);</strong>

This query will generate the following output:

year##2021111002021121502021 1Total25020212312020212413020212Total250202211 9020221Total90Grand Total630## Advantages of rollup:

quarter	month	count(order_id)

Easily create multi-level aggregations.

Allows users to explore data at different granularities.

• Improve query performance because aggregations are calculated in advance.

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