You plan to use Azure Reservations on your Azure SQL Database. To which resource type will the reservation discount be applied?

vCore Compute.

With reserved capacity, you make a commitment for SQL Database and/or SQL Managed Instance use for a period of one or three years to get a significant discount on the compute costs. To purchase reserved capacity, you need to specify the Azure region, deployment type, performance tier, and term.

You do not need to assign the reservation to a specific database or managed instance. 

Matching existing deployments that are already running or ones that are newly deployed automatically get the benefit. 

By purchasing a reservation, you commit to usage for the compute costs for a period of one or three years. As soon as you buy a reservation, the compute charges that match the reservation attributes are no longer charged at the pay-as-you go rates.