Creación de tabla en oracle

CREATE table "S" (
    "A"          NUMBER(5,5) NOT NULL,
    "C"          VARCHAR2(4000),
    constraint  "S_PK" primary key ("A")
)
/

CREATE sequence "S_SEQ" 
/

CREATE trigger "BI_S"  
  before insert on "S"              
  for each row 
begin  
    select "S_SEQ".nextval into :NEW.A from dual;
end;
/   

ALTER TABLE "S" ADD CONSTRAINT "S_FK" 
FOREIGN KEY ("C")
REFERENCES "TABLA1" ("ID")

/