Question

试图让这个查询起作用

SELECT studentid, fName, lName, dob
FROM Student
WHERE courseNo IN
(SELECT courseNo
FROM Student
WHERE courseNo = 1001 IN
(SELECT dob
FROM Student
WHERE dob < `1985-09-12`));

但出于某种原因，它说的是空集？

所有数据都在Student的同一个表中。如果有帮助，dob的格式为YYYY-MM-DD。

Answer 1

我想你想做这样的事情：

SELECT studentid,fName,lName,dob From Student
where courseNo ='1001' and dob<'1985-09-12'

Answer 2

WHERE courseNo = 1001和IN之间缺少一个属性。我不确定你到底需要什么，但也许可能是这样的？：

SELECT studentid, fName, lName, dob
FROM Student
WHERE courseNo IN
(SELECT courseNo
FROM Student
WHERE courseNo = 1001 AND dob IN
(SELECT dob
FROM Student
WHERE dob < '1985-09-12'));

如果是这样，请使查询更简单，它适合您？尝试这样的事情：

SELECT studentid, fName, lName, dob
FROM Student
WHERE courseNo = 1001 and dob < '1985-09-12';

双嵌套选择

2 个答案: