alias some columns names as one field in oracle's join select query

Question

Hi

We are developing something like a social networking website. I've got task to do 'follow me' functionality. In our website objects are users, teams, companies, channels and groups (please don't ask why there are groups and teams - it is complicated for me too, but teams are releated to user's talent)

Users, teams, channels, companies and groups have all their own tables.

I have a query which gets me all the follower's leaders like this

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

I need to get all fields like:

• user_name,
• company_name,
• channel_name,
• group_name,
• team_name

as one field in SELECT's product. I have tried to alias them all the same 'name' but Oracle numbered it. Please help :)

Answer 1

I'm not sure why you need to get them as one field, because aren't you going to need to split the information out on the client side? Anyway, one way you could do it would be like this:

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

This would give you a pipe delimited field called all_fields. If you have multiple user_name fields from different tables, you could use the same approach:

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

You could then split the field on the client side.

Personally, I would just do something like this:

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

In other words, just use a unique column alias for each user_name.

Answer 2

Column names in a query result set must be unique. Perhaps you want one row for each user, company, channel, group and team for the given follower? In which case I'd use a query like this:

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

I got thinking and I come up with this solution:

Is it slower than solution of Jeffrey Kemp?

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