SQL < any <= any返回相同的东西

Question

create table College(cName varchar(100), state varchar(100), enrollment int);
insert into College values ('Stanford', 'CA', 15000);
insert into College values ('Berkeley', 'CA', 36000);
insert into College values ('MIT', 'MA', 10000);
insert into College values ('Cornell', 'NY', 21000);


select cName 
from College S1 
where enrollment <= any (select enrollment 
                             from College S2 
                             where S2.cName <> S1.cName)

select cName 
from College S1 
where enrollment < any (select enrollment
                        from College S2 
                        where S2.cName <> S1.cName)

​

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这两个查询返回相同的东西，我不明白为什么。第一个查询也不返回Berkeley，但不是Berkeley <= Berkeley。

Answer 1

您没有通过执行where S2.cName <> S1.cName来比较匹配cNames的注册值

忽略此条件以查看差异：

select cName 
from College S1 
where enrollment <= any (select enrollment from College S2)

select cName 
from College S1 
where enrollment < any (select enrollment from College S2)

Answer 2

因为在伯克利没有一个值为<= 36000(对应的注册值)，即36000<=(15000,10000,21000)，它不会返回任何值