SQL OVER Function: Purpose Explained

The SQL OVER function is a window function used to calculate the value of aggregate functions in query results. It can execute aggregate functions on each row in the query result and return the result to each row in the result set. Using the OVER function allows for aggregating calculations over the entire result set, not just individual rows.

The OVER function is commonly used in the following scenarios:

1. Calculate aggregated values within rows: for example, calculating the proportion of sales quantity for each product out of the total sales quantity.
2. Calculate moving aggregate values: By specifying a range within the window of the result set, one can calculate moving averages, cumulative sums, and more.
3. Sorting and partitioning: The OVER function can be used to sort and partition the result set, allowing for specific rows or partitions to be considered when performing aggregate calculations.

The basic syntax for the OVER function is as follows:

<aggregate_function>(expression) OVER ([PARTITION BY <partition_column(s)>] [ORDER BY <order_column(s)>])

The is the aggregation function to be executed, the expression is the calculation to be performed, PARTITION BY is used for partitioning, and ORDER BY is used for sorting.

In conclusion, the OVER function can perform flexible aggregate calculations on a result set to obtain more specific and detailed data analysis results.