An easy-to-overlook function in an OLE DB Source adapter is the Preview button.
To tinker with the Preview button, let's first create some dummy data in a Data Flow Task. There are a couple ways to create dummy data in a Data Flow, one way is to use an OLE DB Source. Drag it onto the data flow canvas and open the editor. Select (or create) a Connection Manager and set the Data Access Mode to "SQL command". Enter the following T-SQL statement:
Select 'A' as [Group], 112 as [Number]
Select 'B', 219
Select 'A', 111
Select 'C', 311
Select 'A', 117
Select 'B', 211
Now that we have some dummy data, click the Preview button to get a look at a sample of the data returned - up to 200 rows:
This is some cool functionality - especially when I'm creating aggregates or invoking some Case logic.