Update column with value of another column or another column With PostgreSQL (I'm using the version 9.1) is it possible to do mass update with a single query a column value with the value of another column, but if the other column value is null, to use the value of a third column, and if the third one is absent to use the current datetime (all the column have type timestamp)

I need to change


columnA columnB columnC
null    foo     bar
null    null    baz
null    null    null


to


columnA columnB columnC
foo     foo     bar
baz     null    baz
quz     null    null


where quz is the current datetime.
You can use COALESCE() function to do the update:

UPDATE ...
SET columnA = COALESCE(columnB, columnC, now()); 


COALESCE will return the first non-null value in the list that you provide.