Need to update all entries of one table based on an earlier backup

For reasons best left unmentioned, I need to update entries in a table from a backup; I need to do all entries.

For reasons eluding my sleep deprived eyes this fails in every variation I can think of:

update foo set foo.foo_name2=foo_old.foo_name2 where foo.foo_id = foo_old.foo_id;
ERROR: missing FROM-clause entry for table "foo_old"

Could someone please hit me with a clue-stick ? This is crucial and yet I am stumbling over something. Since I am not updating foo_old I am baffled as to what this messsage really means. I've tried "where foo_old.foo_id = foo.foo_id ... same message.

TIA,

Greg Williamson
Senior DBA
DigitalGlobe

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