oracle(plsql)生成流水号

CREATE OR REPLACE FUNCTION fn_no_make(v_prefix     VARCHAR2,
                                      v_table_name VARCHAR2,
                                      v_number_col VARCHAR2)
 /*
  * v_prefix:     编码前缀两位
  * v_table_name：编码所在表名
  * v_number_col：编码所在列名
  */ 
  RETURN VARCHAR2 IS
  v_old_no   VARCHAR2(50); --原编码
  v_new_no   VARCHAR2(50); --新编码
  v_old_num  NUMBER;       --原编码后三位编号
  v_new_num  VARCHAR2(10); --新编码后三位编号
  v_date_no  VARCHAR2(10); --当前日期编号
  v_sql      VARCHAR2(4000);
BEGIN
  v_sql := ‘SELECT MAX(‘ || v_number_col || ‘) FROM ‘ || v_table_name;
  EXECUTE IMMEDIATE v_sql INTO v_old_no;

  v_sql := ‘SELECT TO_CHAR(SYSDATE,‘‘YYYYMMDD‘‘) FROM DUAL‘;
  EXECUTE IMMEDIATE v_sql INTO v_date_no;

  v_old_num := to_number(substr(v_old_no, 12, 3));
  v_new_num := lpad(to_char(v_old_num+1), 3, ‘0‘);

  IF v_old_no IS NULL OR substr(v_old_no, 3, 8) <> v_date_no THEN
    v_new_no := v_prefix || v_date_no || ‘-‘ || ‘001‘;
  ELSE
    v_new_no := v_prefix || v_date_no || ‘-‘ || v_new_num;
  END IF;

  RETURN v_new_no;
EXCEPTION
  WHEN OTHERS THEN
    dbms_output.put_line(SQLERRM);
END fn_no_make;