Partition By Query Problem

Question

Hi everyone,
I'm trying to print out for every 5 seconds; the average value of each stock's price for last 10 seconds. The query shoud look like this:
select price, avg(price) from stockInputChannel [partition by stockName range 10 slide 5]
BUT, OCEP's CQL does not suppport this kind of query. It warns me to use "partition by $partname rows $rownumber range $rangevalue slide $slidevalue". As I mentioned above I do not need row related query, parameter.. Why the CQL forces me to use that?
Thanks.

Answer 1

Hi,
Peter is right. The best way to learn how a function works is to do some experiments. The SQL Languarge Reference manual describes all the built-in functions, including ROW_NUMBER, and has a good general description of how analytic functions in general work, under "Analytic functions".
ROW_NUMBER assigns an integer 1, 2, 3, ... to each row.
When you say "partition by customer_no", a separate set of numbers (starting with 1) will be used for each distinct value of customer_no.
When you say "order by customer_type desc,rowid desc", that means the lower numbers will be assigned to the higher values of customer_type. If there is a tie (two or more rows with exactly the same customer_type), then lower numbers will be assigned to the higher values of rowid.
In the main query, the WHERE clause includes only the rows that were assigned 1 by the ROW_NUMBER function. The result is get one row of dta for each customer_no (the PARTITION BY column). Which row will that be? The one with the highest customer_type (the ORDER BY column). This is called a Top-N Query, because you are picking N items (N=1 here) from the top of a sorted list. Notice that the analytic function is used in a sub-query, and its value is used in the WHERE clause of the main query. That's necessary, because analytic fucntions in a (sub)query are evaluated after the WHERE clause.