oracle12c中的审核触发器编译时出错

refer my ER

CREATE OR REPLACE TRIGGER EVA 
    AFTER INSERT ON C_EVALUATION
    FOR EACH ROW
    DECLARE
    v_cid number(25);
    v_isbn number(25);
    v_cname VARCHAR2(50);
    v_tittle VARCHAR2(150);
    v_date date;
    v_location VARCHAR2(50);
    v_eva VARCHAR2(250);
    BEGIN
    v_cid:=:OLD.C_ID;
    v_isbn:=:OLD.B_ISBN;
    v_eva:=:OLD.e_desc;

    SELECT C_NAME INTO v_cname FROM C_CUSTOMER WHERE C_ID = v_cid;
    select l_date INTO v_date FROM C_LEND where c_id = v_cid;
    select B_TITTLE INTO v_tittle FROM C_BOOK WHERE B_ISBN = v_isbn;
    SELECT TOWN INTO v_location FROM COPY WHERE B_ISBN = v_isbn;

    IF :NEW.R_ID IS NULL 
    THEN       
        INSERT INTO e_audit (
        c_name,
        b_tittle,
        h_date,
        location,
        evaluation
    ) VALUES (
        v_cname,
        v_tittle,
        v_date,
        v_location,
        v_eva
    );
    END IF;
    END;
    /

在账表中给出了评估,但评估、费率应由客户给出,如果客户将费率作为空值给出,则以下触发器应起作用。但我们得到了一个错误,因为忽略了语句,表或视图不存在。我检查了两次以上,但所有的表名和ID都很完美。请给我们解决错误的方法