sql - 仅在哪里查询？

Question

在sqlite中有像“ only”这样的关键字吗？我必须写一个查询来显示只保留红船的水手姓名。所以我当前的查询是：

select s.sname
from sailor s, boat b, reservation r
where s.sname = r.sname
and b.bname = r.bname
and b.color = 'red';

上面查询的问题是它还会显示保留红色+其他颜色小船的水手姓名。我的查询结果：

a reserve red boat
a reserve green boat
b reserve red boat

但由于他只保留红船，因此应该只显示b。

Answer 1

您可以使用NOT EXISTS子句仅用red船来过滤水手。

select r.sname
from reservation r
join boat b
on b.bname = r.bname
and b.color = 'red'
and not exists ( select 1 from reservation r2
                 join boat b2
                 on r2.bname = b2.bname
                 and r2.sname = r.sname
                 and b2.color <> 'red' )