[SQL/ORACLE] missing left parenthesis 에러

CREATE TABLE t_board (
    articleno     NUMBER NOT NULL PRIMARY KEY,
    parentno      NUMBER DEFAULT 0 NOT NULL,
    title         VARCHAR2(100) NOT NULL,
    content       VARCHAR2(4000) NOT NULL,
    imagefilename VARCHAR2(100),
    writedate     DATE DEFAULT sysdate NOT NULL,
    writer_id     VARCHAR2(10) NOT NULL,
    CONSTRAINT fk_writer_id FOREIGN KEY ( writer_id )
        REFERENCES t_member ( id )
);

Error report -
ORA-00906: missing left parenthesis
00906. 00000 -  "missing left parenthesis"
*Cause:    
*Action:

create table 할 때 varchar2에 인수로 byte크기를 지정해주지 않으면 missing left parenthesis 에러가 뜬다..
은근히 찾기 어렵네