MySQL left join with multiple views

Question

I have the following query, which I designed to compile data from a number of views based on client data.

SELECT 
  vw_clients.client_id, 
  name, 
  exts, 
  vms, 
  ivrs, 
  queues, 
  conf10, 
  conf20, 
  conf30
FROM 
  vw_clients, 
  vw_exts, 
  vw_vms, 
  vw_ivrs, 
  vw_queues, 
  vw_conf10, 
  vw_conf20, 
  vw_conf30
WHERE 
  vw_clients.client_id = vw_exts.client_id AND 
  vw_clients.client_id = vw_vms.client_id AND 
  vw_clients.client_id = vw_ivrs.client_id AND 
  vw_clients.client_id = vw_queues.client_id AND
  vw_clients.client_id = vw_conf10.client_id AND
  vw_clients.client_id = vw_conf20.client_id AND
  vw_clients.client_id = vw_conf30.client_id;

The query works fine so long as there are records in every view relating to the records in vw_clients. However I need to modify this to use a left join, so that it returns all records from vm_clients and only those from the other views that have records for those clients.

I've read about left joins, but at most I have only found info on joining one or maybe two tables - but I need to join 8. Do I do a left join on vw_clients.client_id to the corresponding client_id field in all of the views? What's the syntax for that?

Would be grateful for any help. I'm very close to solving this issue and I think this is the last piece of the puzzle!

Many thanks.

Answer 1

You can use left join by putting vw_clients in the first in the from list, then all other tables followed after left join. The left join can join only two tables or one "result set" and a table,where the result set is the result of the former join.

In your case:

SELECT 
    T0.client_id, name, exts, vms, ivrs, queues, conf10, conf20, conf30
FROM 
    vw_clients T0
    left join  vw_exts T1 on T0.client_Id=T1.client_id
    Left join  vw_vms T2 on ...
    ...
Where ...

Maybe here you don't need where clause.

Answer 2

Yes, you’d just replace your WHERE with a LEFT JOIN.

LEFT JOIN vw_exts ON vw_clients.client_id = vw_exts.client_id

Then you can remove those extra tables from the FROM part.