General Idea of Aggregation without Aggregator Transformation
Let us take an example: Suppose we want to find the SUM of SALARY for Each Department of the Employee Table. The SQL query for this would be:
SELECT DEPTNO, SUM(SALARY) FROM EMP_SRC GROUP BY DEPTNO;
If we need to implement this in Informatica, it would be very easy as we would obviously go for an Aggregator Transformation. By taking the DEPTNO port as GROUP BY and one output port as SUM(SALARY) the problem can be solved easily.
But we want to achieve this without aggregator transformation!
We will use only Expression transformation to achieve the functionality of Aggregator expression. The trick is to use the very funda of the expression transformation of holding the value of an attribute of the previous tuple over here.
But wait... why would we do this? Aren't we complicating the things here?
Yes, we are! But as it appears, in many cases, it might have an performance benefit (especially if the input is already sorted or when you know input data will not violate the order, like you are loading daily data and want to sort it by day). Please see this article to know more about how to improve the performance of Aggregator transformation
Remember Informatica holds all the rows in Aggregator cache for aggregation operation. This needs time and cache space and this also voids the normal row by row processing in Informatica. By removing the Aggregator with an Expression, we reduce cache space requirement and ease out row by row processing. The mapping below will show how to do this.
Mapping for Aggregation with Expression and Sorter only:
Now I am showing a sorter here just illustrate the concept. If you already have sorted data from the source, you need not use this thereby increasing the performance benefit.
This is how we can implement aggregation without using Informatica aggregator transformation.