Question

I’m working with Rails and I have a Link ActiveRecord model with this table:

create_table "links", :force => true do |t|
  t.string   "name",        :null => false
  t.integer  "sender_id",   :null => false
  t.integer  "receiver_id", :null => false
end

add_index "links", ["name"], :name => "index_links_on_name"
add_index "links", ["sender_id", "receiver_id"], :name => "index_links_on_sender_id_and_receiver_id", :unique => true

What I would like to do is to SELECT every links WHERE name = "follow" which exist from the source to the destination AND from the destination to the source.

For instance, having the following entries:

id | name     | sender_id | receiver_id
---------------------------------------
66 | "follow" | 1         | 2
67 | "follow" | 2         | 1
68 | "follow" | 1         | 3
69 | "fuu"    | 3         | 1
70 | "bar"    | 2         | 25
71 | "bar"    | 25        | 2

…I would like to just get 66 and 67 ids as a result. Because sender_id 1 and receiver_id 67 are linked from source to destination and also from destination to source (with a “follow” name in both cases).

Can we do it, with just one SQL query (in SQL directly or ActiveRecord ORM)? Many thanks!

Answer 1

Try Following Query>>

select * from tablename t1,t2 where t1.sender_id = t2.receiver_id and t2.sender_id=t1.receiver_id and Name like follow"