在oracle的连接选择查询中将某些列名别名为一个字段

Question

我们正在开发类似社交网站的东西。我有任务要做 “跟我来”功能。在我们的网站中，对象有用户、团队、公司、渠道和群组（请不要问为什么有群组和团队——这对我来说也很复杂，但团队与用户的才能有关）

用户、团队、渠道、公司和团体都有自己的桌子。

我有一个查询，可以获取所有追随者的领导者，如下所示，

select
  --fo.leader_id,
  --fo.leader_type,
  us.name as user_name,
  co.name as company_name,
  ch.title as channel_name,
  gr.name as group_name,
  tt.name as team_name
from
  follow_up fo
left join users us
  on (fo.leader_id = us.id and fo.leader_type = 'user')
left join companies co
  on (fo.leader_id = co.user_id and fo.leader_type = 'company')
left join channels ch
  on (fo.leader_id = ch.id and fo.leader_type = 'channel')
left join groups gr
  on (fo.leader_id = gr.id and fo.leader_type = 'group')
left join talent_teams tt
  on (fo.leader_id = tt.id and fo.leader_type = 'team')
where
  follower_id = 83

我需要获取所有字段，例如：

• user_name、
• company_name、
• channel_name、
• group_name、
• team_name

作为 SELECT 产品中的一个字段。 我试图给它们起一个相同的“名字”，但 Oracle 给它编号了。 请帮忙:)

Answer 1

我不确定为什么您需要将它们作为一个字段，因为您不需要在客户端将信息分开吗？无论如何，您可以这样做的一种方法是这样的：

user_name || '|' || company_name || '|' || channel_name || '|' || group_name || '|' || team_name all_fields

这将为您提供一个名为 all_fields 的管道分隔字段。如果您有来自不同表的多个 user_name 字段，您可以使用相同的方法：

   table1.user_name || '|' || table2.user_name ... all_user_names

然后您可以在客户端拆分该字段。

就我个人而言，我会这样做：

    table1.user_name table1_user_name
  , table2.user_name table2_user_name
    ...

换句话说，只需为每个 user_name 使用唯一的列别名。

Answer 2

查询结果集中的列名必须是唯一的。也许您希望给定关注者的每个用户、公司、渠道、组和团队占一行？在这种情况下，我会使用这样的查询：

select fo.leader_type, us.name
from follow_up fo
join users us
  on (fo.leader_id = us.id and fo.leader_type = 'user')
where follower_id = 83
UNION ALL
select fo.leader_type, co.name
from follow_up fo
join companies co
  on (fo.leader_id = co.user_id and fo.leader_type = 'company')
where follower_id = 83
UNION ALL
select fo.leader_type, ch.title as name
from follow_up fo
join channels ch
  on (fo.leader_id = ch.id and fo.leader_type = 'channel')
where follower_id = 83
UNION ALL
select fo.leader_type, gr.name
from follow_up fo
join groups gr
  on (fo.leader_id = gr.id and fo.leader_type = 'group')
where follower_id = 83
UNION ALL
select fo.leader_type, tt.name
from follow_up fo
join talent_teams tt
  on (fo.leader_id = tt.id and fo.leader_type = 'team')
where follower_id = 83

Answer 3

我开始思考并提出了这个解决方案：

它比 Jeffrey Kemp 的解决方案慢吗？

select
  fo.leader_id,
  fo.leader_type,

  case
    when us.subdomain is not null then us.subdomain
    when us2.subdomain is not null then us2.subdomain
    --when co.name is not null then co.name
    when ch.service_url is not null then ch.service_url
    when gr.id is not null then to_char(gr.id)
    when tt.subdomain is not null then tt.subdomain
    else 'nothing!'
    end
    as leader_url,

  case
    when us.name is not null then us.name
    when co.name is not null then co.name
    when ch.title is not null then ch.title
    when gr.name is not null then gr.name
    when tt.name is not null then tt.name
    else 'nothing!'
    end
    as leader_names,

    case
    when us.img_avatar_path is not null then us.img_avatar_path
    when us2.img_avatar_path is not null then us2.img_avatar_path
    --when us.img_avatar_path is not null and fo.leader_id = co.user_id and fo.leader_type = 'company' then us.img_avatar_path
    when ch.default_img is not null then ch.default_img
    when gr.img_avatar_path is not null then gr.img_avatar_path
    when tt.img_avatar_path is not null then tt.img_avatar_path
    else 'nothing!'
    end
    as img_avatar_path,

    case
    when us.img_avatar_x is not null then us.img_avatar_x
    when us2.img_avatar_x is not null then us2.img_avatar_x
    when  ch.default_img_x is not null then ch.default_img_x
    when gr.img_avatar_x is not null then gr.img_avatar_x
    when tt.img_avatar_x is not null then tt.img_avatar_x
    else 0
    end
    as img_avatar_x,

    case
    when us.img_avatar_y is not null then us.img_avatar_y
    when us2.img_avatar_y is not null then us2.img_avatar_y
    when  ch.default_img_y is not null then ch.default_img_y
    when gr.img_avatar_y is not null then gr.img_avatar_y
    when tt.img_avatar_y is not null then tt.img_avatar_y
    else 0
    end
    as img_avatar_y

from
  follow_up fo
  left join users us
  on (fo.leader_id = us.id and fo.leader_type = 'user')
  left join companies co
  on (fo.leader_id = co.user_id and fo.leader_type = 'company')
    left join users us2
    on (co.user_id = us2.id)
  left join channels ch
  on (fo.leader_id = ch.id and fo.leader_type = 'channel')
  left join groups gr
  on (fo.leader_id = gr.id and fo.leader_type = 'group')
  left join talent_teams tt
  on (fo.leader_id = tt.id and fo.leader_type = 'team')
where
  follower_id = :follower_id