Fire trigger on update of columnA or ColumnB or ColumnC

Question

I have the code to fire a trigger only on an update of a single specific column. The trigger is used to fire a function that will raise a postgres \"notify\" event, which I

Answer 1

This is a misunderstanding. The WHEN clause of the trigger definition expects a boolean expression and you can use OR operators in it. This should just work (given that all columns actually exist in the table account_details). I am using similar triggers myself:

CREATE TRIGGER trigger_update_account_details
AFTER UPDATE ON account_details
FOR EACH ROW
WHEN (OLD.email    IS DISTINCT FROM NEW.email
   OR OLD.username IS DISTINCT FROM NEW.username
   OR OLD.password IS DISTINCT FROM NEW.password) 
EXECUTE PROCEDURE notify_insert_account_details();

Evaluating the expression has a tiny cost, but this is probably more reliable than the alternative:

CREATE TRIGGER ... AFTER UPDATE OF email, username, password ...

Because, per documentation:

A column-specific trigger (one defined using the UPDATE OFcolumn_name syntax) will fire when any of its columns are listed as targets in the UPDATE command's SET list. It is possible for a column's value to change even when the trigger is not fired, because changes made to the row's contents by BEFORE UPDATE triggers are not considered. Conversely, a command such as UPDATE ... SET x = x ... will fire a trigger on column x, even though the column's value did not change.

ROW type syntax is shorter to check on many columns (doing the same):

CREATE TRIGGER trigger_update_account_details
AFTER UPDATE ON account_details
FOR EACH ROW
WHEN ((OLD.email, OLD.username, OLD.password, ...)
       IS DISTINCT FROM
      (NEW.email, NEW.username, NEW.password, ...))
EXECUTE PROCEDURE notify_insert_account_details();

Or, to check for every visible user column in the row:

...
WHEN (OLD IS DISTINCT FROM NEW)
...