pg的group by rollup

PostgreSQL的GROUP BY ROLLUP是一种分组函数，它可以在一个SELECT语句中生成多个分组集合的聚合数据。ROLLUP函数可以生成一个包含所有行的总计行，以及每个分组级别的小计行。例如，如果您按年份和月份分组，则ROLLUP函数将生成每个月份的小计行和每年的总计行。GROUP BY ROLLUP的语法如下：

SELECT column1, column2, ..., GROUPING(column1) AS col1_group, GROUPING(column2) AS col2_group, SUM(value) AS total
FROM table_name
GROUP BY ROLLUP(column1, column2, ...)

其中，column1、column2等是要分组的列，value是要聚合的值，GROUPING函数用于确定每个列是否在当前分组级别中，col1_group、col2_group是用于标识每个列是否在当前分组级别中的虚拟列。

相关问题

group by rollup

GROUP BY ROLLUP is a clause used in SQL to generate multiple levels of subtotals in the result set. It is often used in conjunction with the GROUP BY clause to produce a hierarchical breakdown of data.

When you use GROUP BY ROLLUP, the result set will include additional rows that represent different levels of aggregation. These rows will contain NULL values in the columns that represent higher-level aggregations.

For example, consider a table "Sales" with columns "Region", "Country", and "Product". If you want to get subtotals at the region, country, and product levels, you can use the GROUP BY ROLLUP clause like this:

SELECT Region, Country, Product, SUM(SalesAmount) AS TotalSales
FROM Sales
GROUP BY ROLLUP (Region, Country, Product);

The result set will include rows for each combination of region, country, and product, as well as subtotals for each level of aggregation. The rows representing higher-level aggregations will have NULL values in the corresponding columns.

Note that the number of rows returned can be significantly larger when using GROUP BY ROLLUP compared to a simple GROUP BY clause. Therefore, it's important to consider the performance implications when using this feature.

oracle group by rollup

Oracle中的GROUP BY ROLLUP是一种用于生成分组汇总报表的查询语句。它可以根据指定的列进行分组，并在每个分组上生成汇总数据。ROLLUP操作会生成多个层次的汇总结果，从最粗粒度到最细粒度。

例如，假设我们有一个销售表，其中包含了产品、地区和销售额等信息。我们可以使用GROUP BY ROLLUP来生成按产品、地区和总体销售额进行汇总的报表。

下面是一个示例查询语句：

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

这个查询将会生成以下结果：

- 按产品和地区进行分组的汇总结果
- 按产品进行分组的总体汇总结果
- 总体汇总结果

这样我们就可以一次性获取到不同层次的汇总数据，方便进行分析和报表生成。