【MYSQL】一直以为下面这条语句会出错，但是执行没错误！

[糖炒唐朝栗子]

一直以为下面这条语句会出错，但是执行没错误
SELECT article, dealer, price
FROM shop s1
WHERE price = (SELECT MAX(s2.price)
FROM shop s2
WHERE s1.article = s2.article);

SELECT article, dealer, price
FROM shop s1
WHERE price in (SELECT MAX(s2.price)
FROM shop s2
WHERE s1.article = s2.article);

括号中内容是上面子查询的结果：
select * from shop where price = (3.99,10.99,1.69,19.95);//出错
select * from shop where price in (3.99,10.99,1.69,19.95);

语句一的子查询是查出一个就比较 还是全查出来再进行比较，

[ACMAIN_CHM]

SELECT article, dealer, price FROM shop s1 WHERE price = (SELECT MAX(s2.price) FROM shop s2 WHERE s1.article = s2.article); 红色部门只会返回一个值。

[糖炒唐朝栗子]

引用 1 楼 ACMAIN_CHM 的回复:

SELECT article, dealer, price FROM shop s1 WHERE price = (SELECT MAX(s2.price) FROM shop s2 WHERE s1.article = s2.article); 红色部门只会返回一个值。

这条语句会执行几次？是article的个数?

[ACMAIN_CHM]

会执行SELECT article, dealer, price FROM shop s1这么多次。

[二月十六]

那个语句每次只会返回一个值，如果没有加max返回的会是个集合，加了max就是每次返回符合条件的最大值