Toad对Oracle格式化程序的建议

警告是什么意思?

为什么第二个例子比第一个更糟?

SELECT   product_id, prod.name name, sample_id
  FROM   lims.sample JOIN lims.product prod USING (product_id)

VS

SELECT   product_id, prod.name name, sample_id
  FROM   (SELECT   sample_id, product_id FROM lims.sample)
         JOIN lims.product prod
/* ADVICE: [131]  This item has not been declared, or it refers to a label */
            USING (product_id)

/* ADVICE:
ADVICE SUMMARY

Count  Recommendation
-----  --------------
    1  [131]  This item has not been declared, or it refers to a label
                  The Oracle equivalent error messages are  PLS-00320 and
                  PLS-0321.
*/

仅供参考:两个查询都运行良好,并返回相同的结果。