CREATE TABLE REG$ABONENT$EQUIPMEN2 (
    ID     D_KEY NOT NULL,
    ABOUT  COMPUTED BY ('My ID is ' || ID),
    NAME   COMPUTED BY ((SELECT FIRST 1 'NAME' FROM DIR$EQUIPMENT$KIND))
);

ALTER TABLE REG$ABONENT$EQUIPMEN2 ADD CONSTRAINT PK_REG$ABONENT$EQUIPMEN2 PRIMARY KEY (ID);

SET TERM ^ ;

CREATE OR ALTER TRIGGER REG$ABONENT$EQUIPMEN2_BU0 FOR REG$ABONENT$EQUIPMEN2
ACTIVE BEFORE UPDATE POSITION 0
AS
BEGIN
    EXECUTE PROCEDURE PKG$EXCEPTION.FOR_EQUIPMENT(NEW.ID, 'update');
END^

SET TERM ; ^

    PROCEDURE FOR_EQUIPMENT(ID_EQUIPMENT DOM$KEY NOT NULL, TEXT DOM$TEXT_EXCEPTION NOT NULL)
    AS
    BEGIN
        EXCEPTION EXC$ERROR COALESCE((SELECT ABOUT FROM REG$ABONENT$EQUIPMEN2 WHERE ID = :ID_EQUIPMENT), '<Название пусто> (ID = ' || :ID_EQUIPMENT || ')') || '.' || :TEXT || '.';
    END

UPDATE REG$ABONENT$EQUIPMEN2 SET ID = ID

EXC$ERROR.
<Название пусто> (ID = 500).update.
At procedure 'PKG$EXCEPTION.FOR_EQUIPMENT' line: 20, col: 9
At trigger 'REG$ABONENT$EQUIPMEN2_BU0' line: 5, col: 5.

EXC$ERROR.
My ID is 500.update.
At procedure 'PKG$EXCEPTION.FOR_EQUIPMENT' line: 20, col: 9
At trigger 'REG$ABONENT$EQUIPMEN2_BU0' line: 5, col: 5.