SQL 查询：如何Select每组连接表的最大值

Question

我有这个问题，当这个 table 加入另一个 table 称为 tblClubs（有 9 条记录）。

tblPlayers 字段是：

ID(Autonumber) | CLubID(Number) | Player Name(Text) | PlayerAge(Number)

tblClubs 字段是：

ID(Autonumber) | ClubName (Text)

现在我需要在他们自己俱乐部的其他球员中显示年龄最大的球员姓名以及旁边的俱乐部名称，如下所示：

Club Name | Player Name | Maximum Age (older player of each club)

请告诉我怎么做？

Answer 1

您可以使用 window 函数解决此问题，如果您的数据库支持它们：

select c.club_name, p.player_name, p.player_age
from clubs c 
inner join (
    select 
        p.*, 
        rank() over(partition by p.club_id order by p.player_age desc) rn 
    players p
) p on p.club_id = c.id and p.rn = 1

一个常见且非常便携的替代方法是使用子查询进行过滤：

select 
    c.club_name, 
    t.player_name,
    t.player_age
from players p
inner join clubs c on c.id = p.club_id
where p.age = (select max(p1.age) from players p1 where p1.club_id = p.club_id)

Answer 2

SQL Fiddle

MS SQL Server 2017 架构设置:

CREATE TABLE tblPlayers (ID INT, ClubID INT,PlayerName VARCHAR(255)
                         ,PlayerAge INT)
CREATE TABLE tblClubs (ID int,ClubName VARCHAR(255))   

INSERT INTO tblPlayers(ID,ClubID,PlayerName
                       ,PlayerAge) VALUES (1,1,'John',30)
                       ,(2,1,'Mark',25)
                       ,(3,1,'Albert',36)
                       ,(4,2,'David',33)
                       ,(5,2,'John',31)
INSERT INTO tblClubs(ID, ClubName) VALUES(1,'TEAM 1')
                                  ,(2,'TEAM 2')

查询 1:

SELECT
    *
FROM
    (SELECT A.*,RANK() OVER 
     (PARTITION BY A.ClubID ORDER BY A.PlayerAge desc) as rn
    FROM tblPlayers A
    INNER JOIN tblClubs B ON A.ClubID=B.ID) t
WHERE
    t.rn = 1

Results:

| ID | ClubID | PlayerName | PlayerAge | rn |
|----|--------|------------|-----------|----|
|  3 |      1 |     Albert |        36 |  1 |
|  4 |      2 |      David |        33 |  1 |

SQL 查询：如何Select每组连接表的最大值

SQL Query : how to Select Maximum value of each group of joined tables

sql

join

subquery

greatest-n-per-group