Verificar si existe una fila en una tabla

SELECT count(1) from table where key = value;

declare @_var INT = 0
 set @_var = (select count(1) from SQLTabla where folio = 11801 and RUT_proveedor = '123456-0')
 print @_var

select @EmpID = ID from dbo.Employee

Or

set @EmpID =(select id from dbo.Employee)

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