Update MyTable
Set Value = (
Select Min( T2.Value )
From MyTable As T2
Where T2.Id <> MyTable.Id
And T2.Name = MyTable.Name
)
Where ( Value Is Null Or Value = '' )
And Exists (
Select 1
From MyTable As T3
Where T3.Id <> MyTable.Id
And T3.Name = MyTable.Name
)