请教这个需求的SQL怎么写,谢谢! - V2EX
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gaolinjie
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请教这个需求的SQL怎么写,谢谢!

  •  
  •   gaolinjie 2013-10-20 11:51:25 +08:00 2592 次点击
    这是一个创建于 4379 天前的主题,其中的信息可能已经有所发展或是发生改变。
    表 follow
    +----+---------+------------+---------------------+
    | id | user_id | channel_id | created |
    +----+---------+------------+---------------------+

    表 channel
    +----+---------+------------+---------------------+
    | id | name | created |
    +----+---------+------------+---------------------+

    现在需要
    1. 先从 follow 表中选择 user_id=xxx 的所有记录,
    2. 然后再从原来的 follow 表中选出 channel_id 不等于1步骤中选出的所有记录的 channel_id 的记录
    3. 最后从 channel 表中选出所有 id 和2步骤中选出的记录的 channel_id 相等的记录

    请教只用一句的SQL语句怎么写? 谢谢!
    4 条回复    1970-01-01 08:00:00 +08:00
    yangqi
        1
    yangqi  
       2013-10-20 12:08:53 +08:00   1
    SELECT id FROM channel WHERE channel_id IN ( SELECT channel_id FROM follow WHERE user_id != 'xxx' )
    zxy
        2
    zxy  
       2013-10-20 12:17:09 +08:00   1
    很久没写了,不知对错,还望指正
    1、若channel_id 不重复,应该可以用这个
    select *
    from
    channel
    where channel_id in (select chnnel_id from follow where user_id <>'xxx')
    2、若channel_id 重复,改为
    select *
    from
    channel
    where channel_id in
    (select chnnel_id
    from
    follow
    where channel_id not in
    (select
    channel_id
    from
    follow
    where user_id ='xxx')
    yangqi
        3
    yangqi  
       2013-10-20 12:52:42 +08:00   1
    读了N遍终于看懂楼主的意思了, 你给的步骤太复杂了,

    直接 SELECT id FROM channel WHERE channel_id NOT IN ( SELECT channel_id FROM follow WHERE user_id = 'xxx' )
    thinkif
        4
    thinkif  
       2013-10-20 13:09:04 +08:00   1
    select id, name, created from channel where exists(select 1 from follow where follow.channel_id = channel.id and user_id<>'xxx')

    用 exists 比 In 快些
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