Tuning SQL statement performance

Question

I have two queries that return same results:

1.

SELECT DISTINCT 
         cvc.object_id
        , cvc.object_name  
 FROM ems.ibo_sm_cvc_rfs cvc,  
      ems.ibo_alcatel_mse_locale poi, 
      ems.ibo_nbn_csa csa, 
      ems.ibo_sm_ean_service_sites_rfs sites, 
      ems.ibo_sm_ean_service_site_rfs site  
WHERE poi.object_name ='testPoi'  
  AND csa.parent_id = poi.object_id  
  AND cvc.csa_id = csa.csa_id  
  AND sites.parent_id = cvc.object_id  
  AND site.service_site_type = 'testSite'  
  AND site.object_name IN (SELECT mse_chassis.object_name  
                             FROM ems.ibo_alcatel_mse_chassis mse_chassis  
                            WHERE mse_chassis.parent_id = poi.object_id);

2. :

SELECT cvc.object_id,
       cvc.object_name
  FROM ems.ibo_sm_cvc_rfs cvc
  JOIN ems.ibo_nbn_csa csa
    ON cvc.csa_id = csa.csa_id
  JOIN ems.ibo_sm_ean_service_sites_rfs sites
    ON sites.parent_id   = cvc.object_id
 WHERE csa.parent_id IN (SELECT poi.object_id
                           FROM ems.ibo_alcatel_mse_locale poi
                          WHERE poi.object_id IN (SELECT csa.parent_id FROM ems.ibo_nbn_csa csa)
                             AND poi.object_name = 'testPoi'
                             AND poi.object_id  IN 
                                 (SELECT mse_chassis.parent_id
                                    FROM EMS.ibo_alcatel_mse_chassis mse_chassis
                                   WHERE mse_chassis.object_name IN
                                         (SELECT site.object_name
                                            FROM EMS.ibo_sm_ean_service_site_rfs site
                                           WHERE site.service_site_type = 'testSite')
                                 )
                         );

Odd for me is that first statement finish in 0.156 seconds while the second one in 0.624 seconds. Need to mention that all ems.* objects are views and I looked that basically every column in where clause is indexed. If necesary I could put the views schema, but I rather not because is company information. Maybe a pair of experience eyes may see an improvment of both of these statements

Answer 1

As @Mihai pointed, your second query is full of subqueries and again I would go one step further to fine tune your first posted query like below

SELECT DISTINCT 
    cvc.object_id
    , cvc.object_name  
FROM ems.ibo_sm_cvc_rfs cvc 
    JOIN ems.ibo_nbn_csa csa ON cvc.csa_id = csa.csa_id
    JOIN ems.ibo_alcatel_mse_locale poi ON csa.parent_id = poi.object_id 
    JOIN ems.ibo_sm_ean_service_sites_rfs sites ON sites.parent_id = cvc.object_id 
    JOIN EMS.ibo_alcatel_mse_chassis mse_chassis ON mse_chassis.parent_id = poi.object_id
    JOIN EMS.ibo_sm_ean_service_site_rfs site ON site.object_name = mse_chassis.object_name
WHERE poi.object_name ='testPoi' 
AND site.service_site_type = 'testSite';

Notice two things:

1. I have modified your implicit join syntax to explicit join syntax

2. I have modified your last subquery with IN clause to a JOIN statement