Mysql：从多个连接表中选择特定数据

Question

我在包装我的大脑时遇到了麻烦。该数据是从3个表来（我已经去除了所有不必要的数据可读性更强）：

mysql> describe vulnerability; 
+---------------+------------------+------+-----+---------+----------------+ 
| Field   | Type    | Null | Key | Default | Extra   | 
+---------------+------------------+------+-----+---------+----------------+ 
| vuln_id  | int(10) unsigned | NO | PRI | NULL | auto_increment | 
| severity  | int(10) unsigned | NO |  | NULL |    | 
| host_id  | int(10) unsigned | NO | MUL | NULL |    | 
+---------------+------------------+------+-----+---------+----------------+ 

mysql> describe cve; 
+---------+------------------+------+-----+---------+----------------+ 
| Field | Type    | Null | Key | Default | Extra   | 
+---------+------------------+------+-----+---------+----------------+ 
| cve_id | int(10) unsigned | NO | PRI | NULL | auto_increment | 
| cve  | varchar(15)  | NO |  | NULL |    | 
| vuln_id | int(10) unsigned | NO | MUL | NULL |    | 
| year | int(4) unsigned | YES |  | NULL |    | 
+---------+------------------+------+-----+---------+----------------+ 

mysql> describe host; 
+--------------+------------------+------+-----+---------+----------------+ 
| Field  | Type    | Null | Key | Default | Extra   | 
+--------------+------------------+------+-----+---------+----------------+ 
| host_id  | int(10) unsigned | NO | PRI | NULL | auto_increment | 
| ip_addr  | int(10) unsigned | NO |  | NULL |    | 
+--------------+------------------+------+-----+---------+----------------+ 

我想输出小于2009年与严重程度是由于有漏洞的主机数量= 3 。年份包含在CVE中，该漏洞与vuln_id FK绑定在一起。该漏洞具有严重性，并与host_id FK绑定在一起。这是我到目前为止：

mysql> select count(distinct ip_addr) from host H 
    inner join vulnerability V on H.host_id = V.host_id 
    inner join CVE C on C.vuln_id = V.vuln_id 
    where V.severity = 3 and C.year < 2009; 
+-------------------------+ 
| count(distinct ip_addr) | 
+-------------------------+ 
|     5071 | 
+-------------------------+ 

这告诉我漏洞比2009年更早的主机的总数，这是一个好的开始。但是，我想更进一步，只包含那些有50个或更多漏洞的主机。我不知道如何做到这一点。主机表中的每个主机条目都有多个相应的漏洞条目。我假设我需要在我的where子句中添加一些内容，但我被卡住了。

在此先感谢。请让我知道是否需要更多信息。

Answer 1

尝试使用GROUP BY和HAVING：

SELECT ip_addr 
FROM host AS H 
INNER JOIN vulnerability AS V 
    ON H.host_id = V.host_id 
INNER JOIN CVE AS C 
    ON C.vuln_id = V.vuln_id 
WHERE V.severity = 3 AND C.year < 2009 
GROUP BY ip_addr 
HAVING COUNT(DISTINCT vuln_id) >= 50 

只得到计数包装其他查询中上面的查询：

SELECT COUNT(*) FROM 
(
    SELECT ip_addr 
    FROM host AS H 
    -- etc... same query as above 
) T1