NEW reflects what the row will look like after the UPDATE. There is no way to tell which columns were specified in the SET clause of the UPDATE; a column which is omitted from that clause will look exactly the same as a column which is set to the value it already had.
Thanks a lot for clarifying this ... my logic was flawed. At stackoverflow.com I found an example which suggested testing against NULL would allow this and I just relied on it.
Here is what I am trying to achieve: Set "synced" to false at any update, except when it has been set explicitly to true. This does not seem to be possible, without checking the value SET by UPDATE?
