Use OQL for this. It is faster than any microflow. Download the oql-module from the Appstore and use the ExecuteOQLStatement.
For finding out your OQL, go to the OQL playground https://mydemoversion8-sandbox.mxapps.io/p/OQL
You will need something like:
Select k.email email count(o.TotalAmount) NumofOrders from "AppstoreAppDemos.Customer" k join "k/AppstoreAppDemos.Order_Customer/AppstoreAppDemos.Order" o group by email;
A Work around solution for this would be to retrieve all the EmployeeSympton List objects sorted via Email.
Loop through the List and check if the their exists another object with the same email id .
If it doesn’t exist then count else don’t count.