sum和sum over

`SUM` 和 `SUM OVER` 都是 SQL 中用于计算数值总和的聚合函数，但它们用法和应用场景有所不同。

`SUM` 是一种基础的聚合函数，当你对一组数值进行求和时，可以直接应用到 SELECT 语句的 SELECT 列上。例如：

SELECT SUM(column_name)
FROM table_name;

这会返回指定列所有值的总和。

而 `SUM OVER`（也称为窗口函数）则是用于在一个"窗口"（由 PARTITION BY、ORDER BY 或 ROLLING/WINDOW BY 子句定义）内计算累计总和。比如，你想看某个字段在某一范围内的累加和：

SELECT column_name,
       SUM_OVER(column_name) OVER (PARTITION BY group_column ORDER BY date_column)
FROM table_name;

这里，`SUM_OVER` 计算了每个 `group_column` 分区内，按照 `date_column` 排序的 `column_name` 的累积和。

窗口函数在分析数据趋势、排名、滑动平均等场景特别有用。

相关问题

mysql sum over

可以回答这个问题。MySQL 中的 SUM() 函数用于计算指定列的总和。而 OVER 子句用于在计算总和时指定分组。例如，可以使用以下语句计算每个部门的销售总额：

SELECT department, SUM(sales) OVER (PARTITION BY department) as total_sales FROM sales_data;

这将返回一个结果集，其中包含每个部门的名称和销售总额。

Oracle sum over

Oracle's `SUM()` function can be used with the `OVER()` clause to calculate a sum of a column's values for each row in a result set. The syntax for using `SUM()` with `OVER()` is as follows:

SELECT column1, column2, SUM(column3) OVER (PARTITION BY column4) as sum_column3
FROM table_name;

In this example, `column1` and `column2` are the columns you want to select from the table, `column3` is the column you want to sum, and `column4` is the column you want to partition by. The `PARTITION BY` clause divides the result set into partitions based on the values in `column4`. The `SUM()` function calculates the sum of `column3` for each partition created by `column4`. The result set includes all columns selected (`column1`, `column2`, and `sum_column3`).

Note that the `OVER()` clause can also be used with other aggregate functions such as `AVG()`, `MIN()`, and `MAX()`.