Postgres - How to reference outer table in update subquery?

Question

I'm trying to do something like the following:

UPDATE table1
SET table1.nearest_city_id = subquery.id
FROM 
  (SELECT id FROM cities ORDER BY cities.location <-> table1.location LIMIT 1)
  AS subquery;

ie set the nearest city in table 1 based on a spatial query..

But I can't reference the row I'm updating within the subquery. Any way around this?

Answer 1

Something like this:

UPDATE table1
  SET nearest_city_id = (select id
                         from cities c
                         ORDER BY c.location <-> table1.location
                         LIMIT 1);

Answer 2

If you need update 1 column of table1 by 1 column of table2 by one condition :

UPDATE Table1 
 SET Table1.Column = A.Column 
      FROM(SELECT Column,Id FROM Table2) As A
 WHERE Table1.Id=Table2.Id