mysql - SQL：使用复杂连接选择外部记录

Question

我想随机选择一个“站点”记录，然后为其获取相关的“渠道”。这是我尝试过的不起作用的方法。请帮忙。谢谢！

    SELECT A.*, B.*
    FROM (
        SELECT companies.company_name, sites.id
        FROM sites
        INNER JOIN company_sites ON company_sites.site_id = sites.id
        INNER JOIN companies ON companies.id = company_sites.company_id
        WHERE sites.active = 1
        AND sites.stage_id = 5
        GROUP BY sites.id
        ORDER BY RAND()
        LIMIT 1
    )A
    JOIN ( 
        SELECT 
        channels.id
        FROM channels 
        WHERE channels.site_id = A.sites_id
    ) B ON 1 = 1 

Answer 1

试试这个：

SELECT just the fields you need
FROM (
    SELECT companies.company_name, sites.id id
    FROM sites
    INNER JOIN company_sites ON company_sites.site_id = sites.id
    INNER JOIN companies ON companies.id = company_sites.company_id
    WHERE sites.active = 1
    AND sites.stage_id = 5
    GROUP BY sites.id
    ORDER BY RAND()
    LIMIT 1
)A
join channels on channels.site_id = id

Answer 2

顺便说一句，如果您只想要每个站点上的频道列表，您可以将它们连接到一个字段中（而不是将它们放在单独的行中）。查询会更简单：

    SELECT companies.company_name, sites.id, group_concat(channels.id) as channels
    FROM sites
    INNER JOIN company_sites ON company_sites.site_id = sites.id
    INNER JOIN companies ON companies.id = company_sites.company_id
    inner join channels on channels.site_id = sites.id
    WHERE sites.active = 1
    AND sites.stage_id = 5
    GROUP BY sites.id
    ORDER BY RAND()
    LIMIT 1