query taking lot of time

Hi pls,, tell me why below query is taking lot of time. pls optimise this query .


NHV_ELEMENT_FOR_USER B is the master table which have each and every record (element Id present in other tables)





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SELECT distinct B.ELEMENT_ID,B.SYS_NAME,B.ALIAS,B.IF_TYPE,
(SUM(A.MEMORYUTILIZATION)) as MemoryUTILISATION,
SUM(A.PHYSICALMEMORYUSED) as PHYSICALMEMORYUSED,E.CALENDAR_DATE,
to_date(A.SAMPLE_TIMESTAMP) as SAMPLE_TIMESTAMP1,
SUM(A.CPUUTILIZATION) as CPUUTILISATION,
SUM(C.BITSIN) as BITSIN,SUM(C.BITSOUT) as BITSOUT,
SUM(C.BYTESIN) as BYTESIN,SUM(C.BYTESOUT) as BYTESOUT,
SUM(C.BITPERSECIN) as BITSPERSECIN,
SUM(C.BitPerSecOut) as BITPERSECOUT,
to_Date(C.SAMPLE_TIMESTAMP) AS SAMPLE_TIMESTAMP2
,to_DATE(D.SAMPLE_TIMESTAMP) as SAMPLE_TIMESTAMP3,
SUM(D.CPUSYSTEMUTILIZATION) as CPUSYSTEMUTILISATION,
SUM(D.MEMORYUTILIZATION) as MEMORYUTILIZATION
from NHV_ELEMENT_FOR_USER B
left join NHV_ST_B_104022 A on B.ELEMENT_ID = A.ELEMENT_ID
LEFT JOIN NHV_ST_B_104050 C on B.ELEMENT_ID = C.ELEMENT_ID
LEFT JOIN NHV_ST_B_104025 D on D.ELEMENT_ID = B.ELEMENT_ID
INNER join NH_DATE_DIM E On to_date(D.SAmple_timestamp) = E.CALENDAR_DATE
OR to_date(A.SAmple_timestamp) = E.CALENDAR_DATE
OR to_date(C.SAmple_timestamp) = E.CALENDAR_DATE
group by B.ELEMENT_ID,B.SYS_NAME,B.ALIAS,B.IF_TYPE,
E.CALENDAR_DATE,to_date(A.SAMPLE_TIMESTAMP),
to_Date(C.SAMPLE_TIMESTAMP),
to_DATE(D.SAMPLE_TIMESTAMP)
order by 2,4,3