SQL重复连接（M:N）

如何在SQL中将一个表与另一个表连接多次？示例：

表“夫妇”：

表“信息”：

现在我需要一个组合结果，它必须是“最新的”（Info.seasure必须是可能的最高值，但不能删除过时的行）：

预期结果：

+-------------+------------+----------+-------------+------------+----------+
| FirstName_1 | LastName_1 | Gender_1 | FirstName_2 | LastName_2 | Gender_2 |
+-------------+------------+----------+-------------+------------+----------+
| Jon         | Targaryen  | Male     | Daenerys    | Targaryen  | Female   |
+-------------+------------+----------+-------------+------------+----------+

---

我不知道如何解决这个问题，ID不是唯一的，我需要“多次”加入Info表。

您可以使用SQL窗口函数选择球员的最新状态，按赛季对每个球员进行排序。然后，您需要为夫妻中的每个人将信息表连接到

couples

表

actor\u最新版本

CTE 结果SQL 结果

---

第一步：加入表一次，并确保为其添加别名。发布加入onceWelcom David的代码！请解释一下获得所需结果背后的逻辑这是一个说明性的例子，但我需要它来处理更复杂的问题，我需要加入它22次。逻辑是我需要一份足球比赛的报告，里面只有球员的身份证和比赛日期。我必须用每个球员的更多信息来替换ID，但这些信息必须与比赛日期相关。用你正在使用的数据库标记你的问题。这个答案是正确的——尽管OP可能使用的是不支持窗口功能或CTE的旧版本MySQL。

+-----+-----------+-----------+--------+--------+
| ID  | FirstName | LastName  | Gender | Season |
+-----+-----------+-----------+--------+--------+
| 123 | Jon       | Snow      | Male   |      6 |
| 456 | Daenerys  | Targaryen | Female |      6 |
| 123 | Jon       | Targaryen | Male   |      7 |
+-----+-----------+-----------+--------+--------+

+-------------+------------+----------+-------------+------------+----------+
| FirstName_1 | LastName_1 | Gender_1 | FirstName_2 | LastName_2 | Gender_2 |
+-------------+------------+----------+-------------+------------+----------+
| Jon         | Targaryen  | Male     | Daenerys    | Targaryen  | Female   |
+-------------+------------+----------+-------------+------------+----------+

ID  FIRSTNAME   LASTNAME    GENDER  SEASON  LAST_CHANGE
123 Jon         Targaryen   Male    7       1
123 Jon         Snow        Male    6       2
456 Daenerys    Targaryen   Female  6       1

with actor_latest (id, firstname,lastname,gender,season, last_change) as (
    select
        id
      , firstname
      , lastname
      , gender
      , season
      , rank() over (partition by id order by season desc) as last_change
    from info
)
select
    left_partner.firstname as firstname_1
  , left_partner.lastname as lastname_1
  , left_partner.gender as gender_1
  , left_partner.season as season_1
  , right_partner.firstname as firstname_2
  , right_partner.lastname as lastname_2
  , right_partner.gender as gender_2
  , right_partner.season as season_2
from
    couples c
    join actor_latest left_partner on c.id_1 = left_partner.id and left_partner.last_change=1
    join actor_latest right_partner on c.id_2 = right_partner.id and left_partner.last_change=1

FIRSTNAME_1 LASTNAME_1 GENDER_1 SEASON_1 FIRSTNAME_2    LASTNAME_2  GENDER_2 SEASON_2
Jon         Targaryen  Male     7        Daenerys       Targaryen   Female   6