I need a simple query

Hi Mark,

First read excel data into datatable then query your sql table from database and store in datatable then using linq query you can query from both datatable and mark boolean field as per your requirement based on query,

Read data from Excelsheet,

https://www.c-sharpcorner.com/UploadFile/75a48f/read-excel-sheet-data-and-bind-with-asp-net-gridview/

Query two datatable using linq,

https://www.c-sharpcorner.com/UploadFile/0c1bb2/join-two-datatable-using-linq-in-Asp-Net-C-Sharp/

Then you can export that result to excel,

https://www.c-sharpcorner.com/UploadFile/deveshomar/exporting-datatable-to-excel-in-C-Sharp-using-interop/