SQL triple left join query across three databases - sql

Question

I'm trying to run a query across three tables in three different databases. This query works but I'm pulling close to a billion records... Is there any solution to pull the distinct fields from smlog.requestor_type and arcust.maj_class for the following query?
SELECT
smreq.request_id AS ROIrequestID,
arcust.customer AS LAWcustID,
smlog.logid AS ESLlogID,
arcust.maj_class AS invoicetype,
smlog.requestor_type AS SMLrequestortype,
smlog.request_type as SMLrequesttype
FROM roi.sm_request_sp_data reqsp
LEFT JOIN smart.smlog#smartlog smlog ON smlog.logid = reqsp.logid
LEFT JOIN roi.sm_requests smreq ON smreq.request_id = reqsp.request_id
LEFT JOIN lawson.arcustomer#smart7 arcust ON arcust.customer =
smreq.customer_id
WHERE smreq.ORIG_DT >= TO_DATE('2016/03/01', 'yyyy/mm/dd')
AND smreq.ORIG_DT <= TO_DATE('2016/03/02','yyyy/mm/dd')
GROUP BY smlog.requestor_type;

Answer 1

These are observations, not an answer
SELECT
smreq.request_id AS ROIrequestID
FROM roi.sm_request_sp_data reqsp
LEFT JOIN roi.sm_requests smreq ON reqsp.request_id = smreq.request_id
WHERE smreq.ORIG_DT >= TO_DATE('2016/03/01', 'yyyy/mm/dd')
AND smreq.ORIG_DT <= TO_DATE('2016/03/02', 'yyyy/mm/dd')
That LEFT JOIN is overridden completely by the where clause (any NULL produced from the left join is disallowed) so use an INNER JOIN instead.
For the where clause It isn't clear if you want one day's data ('2016/03/01') or 2 day's (both '2016/03/01'+ '2016/03/02'), If you are expecting just one day then don't use <= in the second predicate.
For the rest we really have no factual basis to make recommendations.