CREATE TABLE TBL_CHILD_1 (
    ID           INTEGER NOT NULL,
    FK_SUBCHILD  INTEGER,
    NAME         INTEGER
);

CREATE TABLE TBL_CHILD_2 (
    ID    INTEGER NOT NULL,
    NAME  VARCHAR(10)
);

CREATE TABLE TBL_MAIN (
    ID           INTEGER NOT NULL,
    FK_CHILD_1   INTEGER,
    FK_CHILD_2   INTEGER,
    FK_SUBCHILD  INTEGER,
    NAME         VARCHAR(10)
);

CREATE TABLE TBL_SUB_CHILD (
    ID    INTEGER NOT NULL,
    NAME  VARCHAR(10)
);

/******************************************************************************/
/***                              Primary keys                              ***/
/******************************************************************************/

ALTER TABLE TBL_CHILD_1 ADD CONSTRAINT PK_TBL_CHILD_1 PRIMARY KEY (ID);
ALTER TABLE TBL_CHILD_2 ADD CONSTRAINT PK_TBL_CHILD_2 PRIMARY KEY (ID);
ALTER TABLE TBL_MAIN ADD CONSTRAINT PK_TBL_MAIN PRIMARY KEY (ID);
ALTER TABLE TBL_SUB_CHILD ADD CONSTRAINT PK_TBL_SUB_CHILD PRIMARY KEY (ID);


/******************************************************************************/
/***                              Foreign keys                              ***/
/******************************************************************************/

ALTER TABLE TBL_CHILD_1 ADD CONSTRAINT FK_TBL_CHILD_1_1 FOREIGN KEY (FK_SUBCHILD) REFERENCES TBL_SUB_CHILD (ID);
ALTER TABLE TBL_MAIN ADD CONSTRAINT FK_TBL_MAIN_1 FOREIGN KEY (FK_CHILD_1) REFERENCES TBL_CHILD_1 (ID);
ALTER TABLE TBL_MAIN ADD CONSTRAINT FK_TBL_MAIN_2 FOREIGN KEY (FK_CHILD_2) REFERENCES TBL_CHILD_2 (ID);
ALTER TABLE TBL_MAIN ADD CONSTRAINT FK_TBL_MAIN_3 FOREIGN KEY (FK_SUBCHILD) REFERENCES TBL_SUB_CHILD (ID);