Trigger.. AFTER and BEFORE with specific column changed

*I'm trying to follow this :*


CREATE TRIGGER check_update
    *BEFORE* UPDATE ON accounts
    FOR EACH ROW
    WHEN (OLD.balance IS DISTINCT FROM NEW.balance)
    EXECUTE PROCEDURE check_account_update();

*but with AFTER instead of BEFORE. and I'm keep getting error on or near
WHEN.
does that because i have to use BEFORE ? what if i need to execute the
procedure after updating column and it has really changed.*

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