Como Lidar Com Foreign key

CREATE TABLE PROJ_FUN (

PF_ID INTEGER NOT NULL,
PF_DataEnv VARCHAR(11) NOT NULL,
PF_DataRet VARCHAR(11),
PF_DiasTrar INTEGER,
PF_Fun_ID INTEGER NOT NULL,

CONSTRAINT PK_PROJ_FUN PRIMARY KEY (PF_ID),

CONSTRAINT FK_FUNCIONARIOS FOREIGN KEY (PF_FUN_ID)
REFERENCES FUNCIONARIOS (FUN_ID));