Question

I have a MySQL table which has the following structure:

 mysql> select id,channel,Stats,Bridged from channels;
 +----------+---------------------------------+---------+-------------------------------+
 | id       | channel                         | Stats   | Bridged                       |
 +----------+---------------------------------+---------+-------------------------------+
 | 21523318 | SIP/5602291658-0007f140         | Up      | SIP/X.Y.Z.Q-0007f13f          >      |
 | 21523321 | SIP/X.Y.Z.Q-0007f13f            | Up      | SIP/5602291658-0007f140       |
 | 21523322 | SIP/5154642553-0007f13a         | Up      | SIP/402-0007f135              |
 | 21523323 | SIP/402-0007f135                | Up      | SIP/5154642553-0007f13a       |

Look at each two records, they are paired: for example ID 21523318 has Channel identical with Bridged column from next ID.

My question is: taking into account that the table usually holds several thousands entries, how could I select a single line for each two records?

I mean — once I have the first line and I can verify that the “Bridged” column info exists as “channel” in the db, to display a single line. I can do this recursively (checking for each line if there’s another Bridged channel , but for several thousands it becomes very slow and there are a lot of queries.
I was thinking of doing inner join with the same table on channel=Bridged and then somehow do a group by or something…

Any clues or ideas on how I should proceed?

Answer 1

If channel and bridged are always swapped, this should work for you:

select *
from channels
where id in (
  select min(id)
  from channels
  group by least(channel, bridged), greatest(channel, bridged))