Query optimization in PostgreSQL?

Question

I have following issue in my drupal site which is postgresql db connected

When i export data to csv using following query it is taking longtime to export into csv

SELECT     DISTINCT(a.*),
           c.nid,
           b.uac_inst_campus_cricos 
FROM       uac_export_coursetable_latest AS a 
LEFT JOIN  uac_institutiondata AS c 
ON         c.uac_institutiondata_institution=a.uac_course_institution 
LEFT JOIN  uac_inst_campus_latest AS b 
ON         b.nid=c.nid 
AND        b.uac_inst_furtherinfobox_heading=a.campusname 
WHERE      a.uac_course_institution = '%d' 
AND        intyear12 = 'Yes' 
ORDER BY   uaccoursecode