CREATE TABLE T_
(
    A_ID INTEGER NOT NULL,
    B_ID INTEGER NOT NULL,
    C_ID INTEGER NOT NULL,
    S_DATE DATE NOT NULL,
    F_DATE DATE NOT NULL,
  CONSTRAINT T___PK PRIMARY KEY (A_ID, B_ID, C_ID)
  CONSTRAINT T___FK__GUIDE FOREIGN KEY (A_ID, B_ID)
    REFERENCES GUIDE (A_ID, B_ID) -- обязательно с запретом каскадного изменения
                                  -- иначе возможно рассогласование C_ID
                                  -- относительно (A_ID, B_ID)
);
COMMIT WORK;


CREATE OR ALTER VIEW T
AS
SELECT A_ID, B_ID, C_ID, S_DATE, F_DATE
  FROM T_;
COMMIT WORK;


SET TERM ^;
CREATE OR ALTER TRIGGER TR__T_BIUD
  FOR "T"
  ACTIVE
  BEFORE INSERT OR UPDATE OR DELETE
  POSITION 0
AS
  DECLARE VARIABLE NEW_C_ID INTEGER DEFAULT NULL;
  DECLARE VARIABLE OLD_C_ID INTEGER DEFAULT NULL;
BEGIN
  IF (INSERTING) THEN
    BEGIN
      -- IF (NEW.A_ID IS NULL OR NEW.B_ID IS NULL) THEN
      --   EXCEPTION <какое-то исключение>
      SELECT NULL
        FROM T_
        WHERE A_ID = NEW.A_ID
          AND B_ID = NEW.B_ID
        FOR UPDATE WITH LOCK
        INTO: NEW_C_ID;
      SELECT Max(C_ID)
        FROM T_
        WHERE A_ID = NEW.A_ID
          AND B_ID = NEW.B_ID
        INTO: NEW_C_ID;
      NEW.C_ID = Coalesce(NEW_C_ID, 0) + 1;
      INSERT INTO T_ (A_ID, B_ID, C_ID, S_DATE, F_DATE)
        VALUES (NEW.A_ID, NEW.B_ID, NEW.C_ID, NEW.S_DATE, NEW.F_DATE);
    END
  ELSE IF (DELETING) THEN
    BEGIN
      SELECT NULL
        FROM T_
        WHERE A_ID = NEW.A_ID
          AND B_ID = NEW.B_ID
          AND C_ID >= OLD.C_ID
        FOR UPDATE WITH LOCK
        INTO: NEW_C_ID;
      NEW_C_ID = OLD.C_ID;
      DELETE
        FROM T_
        WHERE A_ID = OLD.A_ID
          AND B_ID = OLD.B_ID
          AND C_ID = OLD.C_ID;
      FOR
          SELECT C_ID
            FROM T_
            WHERE A_ID = OLD.A_ID
              AND B_ID = OLD.B_ID
              AND C_ID > OLD.C_ID
            ORDER BY C_ID
            INTO: OLD_C_ID
        DO
          BEGIN
            UPDATE T_
              SET C_ID = :NEW_C_ID
              WHERE A_ID = OLD.A_ID
                AND B_ID = OLD.B_ID
                AND C_ID = :OLD_C_ID;
            NEW_C_ID = NEW_C_ID + 1;
          END
    END
  ELSE
    UPDATE T_
      SET
        A_ID   = NEW.A_ID,
        B_ID   = NEW.B_ID,
        C_ID   = NEW.C_ID,
        S_DATE = NEW.S_DATE,
        F_DATE = NEW.F_DATE
      WHERE A_ID = OLD.A_ID
        AND B_ID = OLD.B_ID
        AND C_ID = OLD.C_ID;
END^
SET TERM ;^
COMMIT WORK;

      SELECT NULL
        FROM T_
        WHERE A_ID = OLD.A_ID
          AND B_ID = OLD.B_ID
          AND C_ID >= OLD.C_ID
        FOR UPDATE WITH LOCK
        INTO: NEW_C_ID;

      IF (EXISTS (
            SELECT 0
              FROM T_
              WHERE A_ID = OLD.A_ID
                AND B_ID = OLD.B_ID
                AND C_ID = OLD.C_ID)) THEN
        BEGIN
          .
          .
          .
        END