oracle count over partition by,over （Partition by...） of oracle

"COUNT OVER PARTITION BY" is a window function in Oracle that allows you to count the number of rows in a partition. The "OVER" clause specifies the partitioning and ordering of the rows within the partition.

For example, if you have a table of sales data with columns for date, product, and quantity sold, you could use the following query to count the number of sales for each product within each month:

SELECT date, product, quantity_sold, COUNT(*) OVER (PARTITION BY product, TO_CHAR(date, 'YYYY-MM')) as sales_count
FROM sales_data
ORDER BY date, product

In this example, the "PARTITION BY" clause partitions the data by both product and month, and the "COUNT(*) OVER" function counts the number of rows in each partition. The resulting output would include the date, product, quantity sold, and sales count for each row in the table, ordered by date and product.