select a.awb_no from a where NOT EXISTS (select b.awb_no from b where a.awb_no = b.awb_no)
后来听说可以使用集合操作,更简单方便,不仅可以查A中有而B中无,还可以查询A和B的交集,这个集合指令就是EXCEPT、INTERSECT
select awb_no from sd_dtm EXCEPT select awb_no from start
select awb_no from sd_dtm INTERSECT select awb_no from start