Hello

Could someone give me some pointers to improve the speed of this SQL please.  It's taking about 10 minutes to execute on a fast PC using Firebird v1.56.

I am counting the number of messages sent by different methods, for a particular company. A company has a number of contacts and they receive a number of calls during the month.  These calls can generate a number of messages to be sent out.

This has been working fine for many years, but it appears to execute VERY slowly when a Company has many contacts ~800


select m.MSG_TYPE, count (distinct(m.Message_ID)) as MsgCount
from MESSAGES m 

join MESSAGE_LINK ml
  on ml.message_id = m.message_id
 
join CALLS a
 on a.Call_id = ml.call_id   
 
join CONTACTS c
  on c.CONTACT_ID = a.CONTACT_ID 
 
where c.company_id=240 AND
      (m.TIMESTAMP_ADDED >= '2015.06.01' AND m.TIMESTAMP_ADDED < '2015.06.30' ) AND
       m.TX_Code='O' AND 
      
group by m.MSG_TYPE



Here's the plan:

PLAN SORT (JOIN (C INDEX (I_CONTACTS_A),M INDEX (MESSAGES_TIMESTAMP_ADDED_A),ML INDEX (MESSAGE_LINK_MESSAGE_ID_A),A INDEX (PK_CALLS)))

Many thanks

David