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;
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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;
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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

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;
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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().

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。