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

ROLLUP是一种在GROUP BY语句中使用的子句，它可以生成多层次的分组汇总结果。具体来说，ROLLUP会按照指定的列顺序对数据进行分组，并在每个分组级别上计算聚合函数的值。这样可以得到不同层次的分组总计。

例如，如果我们有一个表格包含订单信息，并想要按照客户和产品类别对订单进行分组，并计算每个组合的订单数量，我们可以使用带有ROLLUP的GROUP BY语句来实现。这样，我们可以得到按照客户和产品类别的分组总计，以及总的订单数量。

可以通过在GROUP BY子句中使用ROLLUP(o_name)来实现这个功能。这样会产生多个分组，包括按照o_name分组的结果，以及o_name的总计。在结果集中，可以使用GROUPING函数来判断某一列是否为总计行。

总而言之，使用GROUP BY ROLLUP子句可以实现按照指定列进行多层次的分组，并计算聚合函数的值。这样可以得到不同层次的分组总计。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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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.