In C#, How can I manipulate a SQL query locally with C# code

Question

I'm connected to a database in a C# WPF Project

Aim is to create a dashboard outputting information

I've got StackPanels set up in the XAML and ListViews within the StackPanel

I had created a SQL Query for each ListView, and was told that wasn't very database efficient or code efficient

How do I manipulate an overall SQL query (with a limiting condition) but pulling down a lot of data and filter on elements to tailor the output?

I also need to be able to drill down into the data - as the SQL Query has at the moment a GROUP BY condition grouping on count, so I want to be able to see the data behind the total figures