The following table lists the values for the RDB$TRIGGER_TYPE
    column of the RDB$TRIGGERS system table and the different types
    of triggers they represent.

    Numeric
    Value      Symbolic Value             Description

    1          RDB$K_BEFORE_STORE         Trigger is evaluated before
                                          an INSERT.
    2          RDB$K_BEFORE_ERASE         Trigger is evaluated before
                                          a DELETE.
    3          RDB$K_BEFORE_MODIFY        Trigger is evaluated before
                                          an UPDATE.
    4          RDB$K_AFTER_STORE          Trigger is evaluated after
                                          an INSERT.
    5          RDB$K_AFTER_ERASE          Trigger is evaluated after
                                          a DELETE.
    6          RDB$K_AFTER_MODIFY         Trigger is evaluated after
                                          an UPDATE.