Sql 根据另一列的最大值选择多个列

我有Oracle 11g数据库和以下三个表（简化）：

IP表，包含IP标识符、IP和IP状态以及FQDN。IPs可能会重复

+-------+-------------+-----------+-----------+
| ID_IP |     IP      | IP_STATUS |   FQDN    |
+-------+-------------+-----------+-----------+
|     1 | 192.168.1.1 |         1 | test.com  |
|     2 | 192.168.1.1 |         2 | test.com  |
|     3 | 192.168.1.1 |         3 | test.com  |
|     4 | 10.10.45.12 |         2 | test2.com |
+-------+-------------+-----------+-----------+

VLAN表，包含和VLAN标识符以及VLAN编号

+---------+-------------+
| VLAN_ID | VLAN_NUMBER |
+---------+-------------+
|       1 |           3 |
|       2 |           5 |
|       3 |           7 |
+---------+-------------+

关联VLAN和IP的表：

+-------+---------+
| IP_ID | VLAN_ID |
+-------+---------+
|     1 |       1 |
|     2 |       2 |
|     3 |       3 |
|     4 |       2 |
+-------+---------+

在实际的IP表中，主键是元组（IP，IP_状态）。我的目标是创建一个新表来消除IP_状态，为此，我希望聚合IP并获取VLAN_编号更高的IP的ID_IP和FQDN。SELECT查询的答案如下：

+-------+-------------+-----------+
| ID_IP |     IP      |   FQDN    |
+-------+-------------+-----------+
|     3 | 192.168.1.1 | test.com  |
|     4 | 10.10.45.12 | test2.com |
+-------+-------------+-----------+

我可以使用以下查询获取IP：

SELECT i.IP, max(v.VLAN_ID)
FROM IPS i 
LEFT JOIN VLAN_IP_REL v_i ON i.ID_IP=v_i.ID_IP
LEFT JOIN VLANS v ON v_i.ID_VLAN=v.ID_INSTANCIA
GROUP BY i.IP;

我不知道的是如何获取其他列。我尝试使用如下子查询：

SELECT i.ID_IP, i.IP, i.FQDN 
FROM IPS i
WHERE i.IP IN (
    SELECT i.IP, max(v.VLAN_ID)
    FROM IPS i 
    LEFT JOIN VLAN_IP_REL v_i ON i.ID_IP=v_i.ID_IP
    LEFT JOIN VLANS v ON v_i.ID_VLAN=v.ID_INSTANCIA
    GROUP BY i.IP;
)

但它不起作用，因为子查询返回两个值，我需要max（vlan.vlan_ID）来进行聚合

我怎样才能获得正确的IP_ID

---

谢谢大家!

您可能需要尝试使用子句。大概

WITH IPWITHMAXVLANID(IP, MAXVLAN) AS (
  SELECT i.IP, max(v.VLAN_ID)
   FROM IPS i 
   LEFT JOIN VLAN_IP_REL v_i ON i.ID_IP=v_i.ID_IP
   LEFT JOIN VLANS v ON v_i.ID_VLAN=v.ID_INSTANCIA
   GROUP BY i.IP
)
SELECT i.ID_IP, i.IP, i.FQDN, iml.MAXVLAN
FROM IPS i
INNER JOIN IPWITHMAXVLANID iml on i.IP = imp.IP

---

希望这有帮助。

您可能需要尝试使用子句。大概

WITH IPWITHMAXVLANID(IP, MAXVLAN) AS (
  SELECT i.IP, max(v.VLAN_ID)
   FROM IPS i 
   LEFT JOIN VLAN_IP_REL v_i ON i.ID_IP=v_i.ID_IP
   LEFT JOIN VLANS v ON v_i.ID_VLAN=v.ID_INSTANCIA
   GROUP BY i.IP
)
SELECT i.ID_IP, i.IP, i.FQDN, iml.MAXVLAN
FROM IPS i
INNER JOIN IPWITHMAXVLANID iml on i.IP = imp.IP

---

希望这有帮助。

您可以使用分析子句按

IP

拆分，并按

VLAN\u编号

排序，然后筛选以仅保留每组中的第一行：

SELECT ID_IP, IP, FQDN
FROM (
    SELECT ROW_NUMBER() OVER (PARTITION BY i.IP ORDER BY v.VLAN_NUMBER DESC) AS NB,
     i.ID_IP, i.IP, i.FQDN
    FROM IPS i 
    LEFT JOIN VLAN_IP_REL v_i ON i.ID_IP = v_i.ID_IP
    LEFT JOIN VLANS v ON v_i.VLAN_ID = v.VLAN_ID
) t_a
WHERE NB = 1

---

您可以使用分析子句按

IP

拆分，并按

VLAN\u编号

排序，然后筛选以仅保留每个组中的第一行：

SELECT ID_IP, IP, FQDN
FROM (
    SELECT ROW_NUMBER() OVER (PARTITION BY i.IP ORDER BY v.VLAN_NUMBER DESC) AS NB,
     i.ID_IP, i.IP, i.FQDN
    FROM IPS i 
    LEFT JOIN VLAN_IP_REL v_i ON i.ID_IP = v_i.ID_IP
    LEFT JOIN VLANS v ON v_i.VLAN_ID = v.VLAN_ID
) t_a
WHERE NB = 1