CREATE TABLE PROJECTS
   (    PROJECT_ID NUMBER(19,0),
        NAME VARCHAR2(20 CHAR),
        DATE_CREATED TIMESTAMP(6),
        DEADLINE TIMESTAMP(6),
        CONSTRAINT PROJECT_PK
            PRIMARY KEY (PROJECT_ID)
   );

  CREATE TABLE USERS
   (    USER_ID NUMBER(19,0),
        FIO VARCHAR2(30 CHAR),
        LOGIN VARCHAR2(20 CHAR),
        PASSWORD VARCHAR2(20 CHAR),
        PROJECT_ID NUMBER(19,0),
        CONSTRAINT FK_PROJECT
            FOREIGN KEY (PROJECT_ID)
            REFERENCES PROJECTS(PROJECT_ID)
            ON DELETE SET NULL,
        CONSTRAINT USER_PK
            PRIMARY KEY (USER_ID)
   );

     CREATE TABLE PROJECT_ORDERS
   (    ORDER_ID NUMBER(19,0),
        USER_ID NUMBER(19,0),
        PROJECT_ID NUMBER(19,0),
        TIME TIMESTAMP(6),
        CONSTRAINT USER_ORDER
            FOREIGN KEY (USER_ID)
            REFERENCES USERS(USER_ID)
            ON DELETE CASCADE,
        CONSTRAINT PROJECT_ORDER
            FOREIGN KEY (PROJECT_ID)
            REFERENCES PROJECTS(PROJECT_ID)
            ON DELETE CASCADE,
        CONSTRAINT ORDER_PK
            PRIMARY KEY (ORDER_ID)
   );

  CREATE TABLE BOARD_MESSAGES
   (    MSG_ID NUMBER(19,0),
        TIME TIMESTAMP (6),
        PRIORITY NUMBER(10,0),
        TEXT VARCHAR2(20 CHAR),
        BOARD_ID NUMBER(19,0),
        CONSTRAINT BOARD_MSG_FK
            FOREIGN KEY (BOARD_ID)
            REFERENCES PROJECTS(PROJECT_ID)
            ON DELETE CASCADE,
        CONSTRAINT BOARD_MSG_PK
            PRIMARY KEY (MSG_ID)
   );

  CREATE TABLE CHAT_MESSAGES
   (    MSG_ID NUMBER(19,0),
        AUTHOR NUMBER(19,0),
        TIME TIMESTAMP (6),
        TEXT VARCHAR2(1000 CHAR),
        CHAT_ID NUMBER(19,0),
        CONSTRAINT BOARD_MSG_FK
            FOREIGN KEY (CHAT_ID)
            REFERENCES PROJECTS(PROJECT_ID)
            ON DELETE CASCADE,
        CONSTRAINT BOARD_AUTHOR_FK
            FOREIGN KEY (AUTHOR)
            REFERENCES USERS(USER_ID)
            ON DELETE CASCADE,
        CONSTRAINT CHAT_MSG_PK
            PRIMARY KEY (MSG_ID)
   );