Active and connected transformation
The Rank transformation allows us to select only the top or bottom rank of data. It Allows us to select a group of top or bottom values, not just one value. During the session, the Power Center Server caches input data until it can perform The rank calculations.
Rank Transformation Properties :
• Cache Directory where cache will be made.
• Top/Bottom Rank as per need
• Number of Ranks Ex: 1, 2 or any number
• Case Sensitive Comparison can be checked if needed
• Rank Data Cache Size can be set
• Rank Index Cache Size can be set
Ports in a Rank Transformation :
I : Minimum Port to receive data from another transformation.
O : Minimum Port we want to pass to other transformation.
V : not needed can use to store values or calculations to use in an expression.
R : Only 1 Rank port. Rank is calculated according to it.
The Rank port is an input/output port. We must link the Rank port to another transformation. Example: Total Salary
The Designer automatically creates a ‘RANKINDEX’ port for each Rank transformation. The Power Center Server uses the Rank Index port to store the ranking position for Each row in a group.
For example, if we create a Rank transformation that ranks the top five salaried employees, the rank index numbers the employees from 1 to 5.
• The RANKINDEX is an output port only.
• We can pass the rank index to another transformation in the mapping or directly to a target.
• We cannot delete or edit it.
Rank transformation allows us to group information. For example: If we want to select the top 3 salaried employees of each Department, we can define a group for Department.
• By defining groups, we create one set of ranked rows for each group.
• We define a group in Ports tab. Click the Group By for needed port.
• We cannot Group By on port which is also Rank Port.
Finding Top 5 Salaried Employees
• EMP will be source table.
• Create a target table EMP_RANK_EXAMPLE in target designer. Structure should be same as EMP table. Just add one more port Rank_Index to store RANK INDEX.
• Create the shortcuts in your folder.
1. Open folder where we want to create the mapping.
2. Click Tools -> Mapping Designer.
3. Click Mapping-> Create-> Give mapping name. Ex: m_rank_example
4. Drag EMP from source in mapping.
5. Create an EXPRESSION transformation to calculate TOTAL_SAL.
6. Click Transformation -> Create -> Select RANK from list. Give name and click Create. Now click done.
7. Pass ports from Expression to Rank Transformation.
8. Edit Rank Transformation. Go to Ports Tab
9. Select TOTAL_SAL as rank port. Check R type in front of TOTAL_SAL.
10. Click Properties Tab and Select Properties as needed.
11. Top in Top/Bottom and Number of Ranks as 5.
12. Click Apply -> Ok.
13. Drag target table now.
14. Connect the output ports from Rank to target table.
15. Click Mapping -> Validate
16. Repository -> Save
Create Session and Workflow as described earlier. Run the Workflow and see the data in target table.
Make sure to give connection information for all tables.
2) Example: Finding Top 2 Salaried Employees for every DEPARTMENT
• Open the mapping made above. Edit Rank Transformation.
• Go to Ports Tab. Select Group By for DEPTNO.
• Go to Properties tab. Set Number of Ranks as 2.
• Click Apply -> Ok.
• Mapping -> Validate and Repository Save.
Refresh the session by double clicking. Save the changed and run workflow to see the new result.
Sample Rank Mapping
When the Power Center Server runs a session with a Rank transformation, it compares an input row with rows in the data cache. If the input row out-ranks a Stored row, the Power Center Server replaces the stored row with the input row.
Example: Power Center caches the first 5 rows if we are finding top 5 salaried Employees. When 6th row is read, it compares it with 5 rows in cache and places it in Cache is needed.
1) RANK INDEX CACHE:
The index cache holds group information from the group by ports. If we are Using Group By on DEPTNO, then this cache stores values 10, 20, 30 etc.
• All Group By Columns are in RANK INDEX CACHE. Ex. DEPTNO
2) RANK DATA CACHE:
It holds row data until the Power Center Server completes the ranking and is Generally larger than the index cache. To reduce the data cache size, connect Only the necessary input/output ports to subsequent transformations.
All Variable ports if there, Rank Port, All ports going out from RANK Transformations are stored in RANK DATA CACHE.
Example: All ports except DEPTNO In our mapping example.