請問在這個題中數(shù)據(jù)庫的關系是什么意思
關系sales(product,month,qty,total)記錄了每種產(chǎn)品每月的銷售數(shù)量(qty)和利潤（profit）.下面是表的示例:
Product month qty profit
Sardines April 16 40
Sardines May 14 35
Sardines June 34 75
Anchovies April 23 78
Anchovies May 12 40.8
Anchovies June 20 60.6
Herrings April 12 23.88
Herrings May 23 45.77
Herrings June 19 37.81
(1)針對題中的示例關系,寫出下列SQL語句的查詢結果.
select s1.month,s1.product,s2.product
from sales s1,sales s2
where s1.month=s2.month and s1.qty>s2.qty and s1.profit