相交MySql

我正在尝试获取几个SQL请求的交集。我试过很多命令，但还是卡住了

以下是三个请求

有人有办法帮我吗

一,

二,

三,

---

可以使用联接轻松重写INTERSECT：

SELECT t1.username
from 
 (
   SELECT username
   FROM mdl_user
   INNER JOIN mdl_quiz_grades
   ON mdl_user.id=mdl_quiz_grades.userid
   WHERE mdl_quiz_grades.quiz = 17
 ) as t1
join
 (
   SELECT username
   FROM mdl_user
   INNER JOIN mdl_quiz_grades
   ON mdl_user.id=mdl_quiz_grades.userid
   WHERE mdl_quiz_grades.quiz = 16
 ) as t
on t1.username = t2.username
join
 (
   SELECT username
   FROM mdl_user
   INNER JOIN mdl_quiz_grades
   ON mdl_user.id=mdl_quiz_grades.userid
   WHERE mdl_quiz_grades.quiz = 15
 ) as t3
on t1.username = t3.username

但在您的例子中，它几乎是相同的查询，只是不同的WHERE条件。您可以应用聚合逻辑：

SELECT username
FROM mdl_user
INNER JOIN mdl_quiz_grades
ON mdl_user.id=mdl_quiz_grades.userid
WHERE mdl_quiz_grades.quiz in (15,16,17)
GROUP BY username
HAVING COUNT(*) = 3

如果同一用户ID可能多次进行相同的测验，则需要应用DISTINCT：

HAVING COUNT(DISTINCT quiz) = 3

---

考虑提供一些样本数据和预期结果。

SELECT t1.username
from 
 (
   SELECT username
   FROM mdl_user
   INNER JOIN mdl_quiz_grades
   ON mdl_user.id=mdl_quiz_grades.userid
   WHERE mdl_quiz_grades.quiz = 17
 ) as t1
join
 (
   SELECT username
   FROM mdl_user
   INNER JOIN mdl_quiz_grades
   ON mdl_user.id=mdl_quiz_grades.userid
   WHERE mdl_quiz_grades.quiz = 16
 ) as t
on t1.username = t2.username
join
 (
   SELECT username
   FROM mdl_user
   INNER JOIN mdl_quiz_grades
   ON mdl_user.id=mdl_quiz_grades.userid
   WHERE mdl_quiz_grades.quiz = 15
 ) as t3
on t1.username = t3.username

SELECT username
FROM mdl_user
INNER JOIN mdl_quiz_grades
ON mdl_user.id=mdl_quiz_grades.userid
WHERE mdl_quiz_grades.quiz in (15,16,17)
GROUP BY username
HAVING COUNT(*) = 3

HAVING COUNT(DISTINCT quiz) = 3