Insert or Update

Declare @key int  = 12
Declare @msg nvarchar(max) = 'L2'

begin tran
   if exists (
       select *
       from dbo.Log2Entity with (updlock,serializable)
       where ID = @key
        )
   begin
      update dbo.Log2Entity
      set
        Message = @msg
      where ID =@key
   end
   else
   begin
      insert into dbo.Log2Entity (Message)
      values (@msg)
   end
commit tran