SQL-如何选择为所有模块注册的学生姓名？

Question

学生

+------+-------+--------------------------------------+
| Sid  | sName | content                              |
+------+-------+--------------------------------------+
| 1    |  Tim  | ...                                  |
| 2    | boyo  | ...                                  |
| 3    | Carl  | ...                                  |
| 4    | Life  | ...                                  |
+------+-------+--------------------------------------+

模块

+------+-------+--------------------------------------+
| mID  | mName | content                              |
+------+-------+--------------------------------------+
| 1    | Data  | ...                                  |
| 2    | IT    | ...                                  |
| 3    | Math  | ...                                  |
|      |       | ...                                  |
+------+-------+--------------------------------------+

注册

+------+-------+--------------------------------------+
| sID  | mID   | content                              |
+------+-------+--------------------------------------+
| 1    | 1     | ...                                  |
| 1    | 2     | ...                                  |
| 1    | 3     | ...                                  |
| 3    | 1     | ...                                  |
+------+-------+--------------------------------------+

Answer 1

按学生对数据进行分组，并仅记录与模块总数相同的模块

select s.sname
from students s
join Registration r on s.sid = r.sid
group by s.sname
having count(r.mid) = (select count(mid) from modules)

Answer 2

您可以尝试按SID和NAME分组此查询：

CREATE TABLE STUD (SID INT, SNAME VARCHAR(20));
CREATE TABLE MODU (MID INT, MNAME VARCHAR(20));
CREATE TABLE REGI (SID INT, MID INT);
INSERT INTO STUD VALUES (1,'Tim');
INSERT INTO STUD VALUES (2,'Boyo');
INSERT INTO STUD VALUES (3,'Karl');
INSERT INTO STUD VALUES (4,'Life');
INSERT INTO STUD VALUES (5,'Tim');
INSERT INTO MODU VALUES (1,'Data');
INSERT INTO MODU VALUES (2,'IT');
INSERT INTO MODU VALUES (3,'Math');

INSERT INTO REGI VALUES (1,1);
INSERT INTO REGI VALUES (1,2);
INSERT INTO REGI VALUES (1,3);
INSERT INTO REGI VALUES (3,1);
INSERT INTO REGI VALUES (5,1);
INSERT INTO REGI VALUES (5,2);
INSERT INTO REGI VALUES (5,3);


SELECT A.SID, A.SNAME 
FROM STUD A
INNER JOIN REGI  B ON A.SID = B.SID
GROUP BY A.SID, A.SNAME
HAVING COUNT(*) = (SELECT COUNT(*) AS RC_MODULES FROM MODU)
;

输出：

    SID SNAME
1   1   Tim
2   5   Tim