Okay so that would be option: each unique request number returned from the get items action?
After the get items action, add a select action to grab the request number.
Then, add a compose action, where you union( the output of the select action with itself, to return an array with unique request numbers. This will also eliminate empty records.
Then you give compose action as input for an apply to each loop, where you can use an odata filter query in the sql action, something like: SQLColumnName eq items('Apply_to_each')?['RequestNumber']
On a side note, if you are working with large tables, power automate is not the greatest tool to use, since it will take a very long time to go through the flow, and you might run into throttle limits