You can also update data in a table based on data from another table:

UPDATE person 
SET state_code = cities.state_code 
FROM cities
WHERE cities.city = city;

Here we are joining the person city column to the cities city column in order to get the city's state code. This is then used to update the state_code column in the person table.

You update all rows in table by simply providing a column_name = value:

UPDATE person SET planet = 'Earth';

You can update multiple columns in a table in the same statement, separating col=val pairs with commas:

UPDATE person 
   SET country = 'USA', 
       state = 'NY' 
WHERE city = 'New York';