Can someone please help me optimize this query? Is there a better way to write this query? I am generating a report of transactions ordered by time and with details of the sender and receiver etc.
SELECT distinct a.time::date ||'<br>'||substring(a.time::time::text,1,8) as Time,
CASE WHEN a.what = 0 THEN 'Money Transfer' WHEN a.what = 15 THEN 'Purchase' WHEN a.what = 26 THEN 'Merchant Streamline' WHEN a.what = 13 THEN 'Reversal' END as Transaction_Type ,
c1.account_no as SenderAccount, c2.account_no as RecieverAccount,
b.country as SenderCountry, d.country as RecieverCountry,
b.firstname as SenderFirstName, b.lastname as SenderLastName,
d.firstname as ReceiverFirstName, d.lastname as ReceiverLastName,
a.status as status,
(select sum(td.amount * 0.01) from transaction_data td where td.data_id = a2.id and td.dir = 1 and td.uid = a.target_uid) as ReversedAmount,
(select sum(td.amount * 0.01) from transaction_data td where td.data_id = a2.id and td.dir = 0 and td.uid = a.uid ) as DepositedAmount, a.flags, (a.amount * 0.01) as Amount,
(a.fee * 0.01) as Fee
FROM data a, customerdata b, customerdata d, customer c1, customer c2 , participant p, data a2
WHERE p.id = a.partner_id AND (a.uid = c1.id) AND (a.target_uid = c2.id) and c1.id=b.uid and c2.id=d.uid
and a.confirmation is not null AND (a2.ref_id = a.id) and
((a2.what = 13) or (a2.what = 17) ) ORDER BY time desc ;
(query plan followed)
The expensive operation is the UNIQUE. Are you sure, in terms of business logic, that this is necessary? Is it actually possible to have duplicate transactions at the exact same time, and if so, would you really want to eliminate them?
As an aside, I prefer to have numeric constants like the 'what' field in a small lookup table of two columns (what_code, what_description); it's easier to extend and to document.
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