Question

我正在努力找到在＆＃34;大数据＆＃34;中获得最高分的人的姓名。课程。

我有3个不同的表：

People (id, name, age, address)
---------------------------------------------------
p1  | Tom Martin| 24 | 11, Integer Avenue, Fractions, MA
p2  | Al Smith  | 33 | 26, Main Street, Noman's Land, PA
p3  | Kim Burton| 40 | 45, Elm Street, Blacksburg, VA
---------------------------------------------------

Courses (cid, name, department)
---------------------------------------------------------
c1 | Systematic Torture | MATH
c2 | Pretty Painful     | CS
c3 | Not so Bad         | MATH
c4 | Big Data           | CS
---------------------------------------------------------

Grades (pid, cid, grade)
---------------------------------------------------
p1  |  c1       | 3.5 
p2  |  c3       | 2.5
p3  |  c2       | 4.0
p3  |  c4       | 3.85
---------------------------------------------------

我无法弄清楚如何在不使用任何花哨的SQL功能的情况下找到成绩最高的人。也就是说，我只想使用SELECT，FROM，WHERE，UNION，INTERSECT，EXCEPT，CREATE VIEW和算术比较运算符，如=，＆lt;，＆gt;。我的结果是展示了我试图实现的目标之外的东西。

这是我到目前为止所尝试的：

    CREATE VIEW TEMPFIVE AS 
    SELECT G1.pid FROM Grades AS G1, Grades AS G2 WHERE G1.pid = G2.pid AND G1.cid = G2.cid

  SELECT People.name, Courses.name FROM TEMPFIVE, People, Courses WHERE TEMPFIVE.pid = People.pid AND Courses.name = "Big Data";

+------------+----------+
| name       | name     |
+------------+----------+
| Tom Martin | Big Data |
| Al Smith   | Big Data |
|Kim Burton  | Big Data |
|Kim Burton  | Big Data |
+------------+----------+

Answer 1

最简单的方法是将LIMT 1与ORDER BY DESC子句一起使用：

SELECT p.name, c.name, g.grade 
FROM People AS p
JOIN Grades AS g ON p.id = g.pid
JOIN Courses AS c ON c.cid = g.cid
WHERE c.name = "Big Data"
ORDER BY g.grade DESC LIMIT 1

Answer 2

对于MySql查询结构没有任何想法。所以解释一下。我希望你可以基于此构建查询。

根据他们的关系加入三个表
在where子句
将等级订单设为DESC订单
将限制设置为仅获取第一行。

Answer 3

试试这个

select * from(
select p.id pid,p.name name, p.age age,p.address address, 
c.cid cid, c.name coursname, c.department department,g.grade grade 
from Grades G
left join 
Courses C on g.cid = c.cid
left join
People  p on g.pid = p.id
)a where coursname= 'Big Data' order by grade desc

您可以在where子句

上应用运算符

Answer 4

如果你只想要1条记录，那么GiorgosBestos就是正确的选择。如果你想要领带。意思是如果超过1名学生具有相同的MAX等级，那么您可以按如下方式进行子选择：

SELECT p.name, c.name, g.grade 
FROM
    (
       SELECT c.cid, MAX(g.grade) MaxGrade
       FROM
          Grades g
          INNER JOIN Courses c
          ON c.cid = g.cid
          AND c.name = 'Big Data'
       GROUP BY
          c.cid
    ) m
    INNER JOIN Grades g
    ON g.cid = m.cid
    AND g.grade = m.MaxGrade
    INNER JOIN People p
    ON g.pid = p.id

Answer 5

以下SQL涵盖了两个或更多学生具有相同最高分的情况：

SELECT P.NAME,
       C.NAME,
       G.GRADE
FROM   PEOPLE P
JOIN   GRADES G ON G.PID = P.ID
JOIN   COURSES C ON C.CID = G.CID
WHERE  C.NAME = 'Big data'
AND    G.GRADE = (SELECT MAX(G2.GRADE)
                  FROM   PEOPLE P2
                  JOIN   GRADES G2 ON G2.PID = P2.ID
                  JOIN   COURSES C2 ON C2.CID = G2.CID
                  WHERE  C2.NAME = 'Big data');

它与Matt提出的SQL类似但不完全相同。

SQL - 如何找到成绩最高的人

5 个答案: