How to improve the run time of this query

Question

Is there any way to improve this query,
I have a table which SR_WId with atleast one subtype as 'Break Fix', 'Break/Fix','Break Fix/Corrective Maint','Break Fix-Corrective Maint'. then i can have other subtype as 'Break Fix', 'Break/Fix', 'Follow Up', 'Follw-Up','T&'||'M Break Fix','Break Fix/Corrective Maint','Break Fix-Corrective Maint'.
Let me know if this is okay or to modify it.
SELECT DISTINCT A.SR_WID AS SR_WID
FROM WC_SR_ACT_SMRY_FS A
WHERE EXISTS
(SELECT NULL FROM WC_SR_ACT_SMRY_FS B
WHERE B.ACT_TYPE = 'Maintenance'
AND B.ACT_SUBTYPE in ('Break Fix', 'Break/Fix','Break Fix/Corrective Maint','Break Fix-Corrective Maint') AND B.NBR_OF_ACTIVITIES = 1 AND B.SR_WID = A.SR_WID
GROUP BY B.SR_WID
HAVING COUNT(B.SR_WID) >= 1)
AND A.ACT_TYPE = 'Maintenance'
AND A.ACT_SUBTYPE IN ('Break Fix', 'Break/Fix', 'Follow Up', 'Follw-Up','T&'||'M Break Fix','Break Fix/Corrective Maint','Break Fix-Corrective Maint')

Answer 1

SELECT DISTINCT A.SR_WID AS SR_WID
           FROM WC_SR_ACT_SMRY_FS A
          WHERE EXISTS(
                   SELECT   NULL
                       FROM WC_SR_ACT_SMRY_FS B
                      WHERE B.ACT_TYPE = 'Maintenance'
                        AND B.ACT_SUBTYPE IN
                              ('Break Fix',
                               'Break/Fix',
                               'Break Fix/Corrective Maint',
                               'Break Fix-Corrective Maint')
                        AND B.NBR_OF_ACTIVITIES = 1
                        AND B.SR_WID = A.SR_WID
                   GROUP BY B.SR_WID
                     HAVING COUNT(B.SR_WID) >= 1 )
            AND A.ACT_TYPE = 'Maintenance'
            AND A.ACT_SUBTYPE IN
                  ('Break Fix',
                   'Break/Fix',
                   'Follow Up',
                   'Follw-Up',
                   'T&' || 'M Break Fix',
                   'Break Fix/Corrective Maint',
                   'Break Fix-Corrective Maint');First of all, you can omit the GROUP BY and HAVING part in the sub-select -
we already know thath the only value for B.SR_WID can be A.SR_WID and
COUNT(B.SR_WID) will always be at least 1, otherwise the sub-select will
return nothing.
As a second step, you could transform EXISTS() into IN():
SELECT DISTINCT SR_WID
           FROM WC_SR_ACT_SMRY_FS A
          WHERE SR_WID IN(
                   SELECT B.SR_WID
                     FROM WC_SR_ACT_SMRY_FS B
                    WHERE B.ACT_TYPE = 'Maintenance'
                      AND B.ACT_SUBTYPE IN
                            ('Break Fix',
                             'Break/Fix',
                             'Break Fix/Corrective Maint',
                             'Break Fix-Corrective Maint')
                      AND B.NBR_OF_ACTIVITIES = 1)
            AND ACT_TYPE = 'Maintenance'
            AND ACT_SUBTYPE IN
                  ('Break Fix',
                   'Break/Fix',
                   'Follow Up',
                   'Follw-Up',
                   'T&' || 'M Break Fix',
                   'Break Fix/Corrective Maint',
                   'Break Fix-Corrective Maint');