我创建了测试数据小提琴，并进行了简单易懂的查询以获取所需的数据，即：
SELECT DISTINCT classId,
std.name,
Class.email,
signUpDate
FROM CLASS
INNER JOIN Student std ON std.email = Class.email
WHERE signUpDate IN
(SELECT max(signUpDate)
FROM CLASS
GROUP BY classId)
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