Postgresql cancella record duplicati

Esempio di query SQL per cancellare records duplicati in postgresql

DELETE
 FROM downloads
 WHERE itemid NOT IN
 (SELECT MAX(dtupla.itemid)
 FROM downloads As dtupla
 GROUP BY dtupla.email,  dtupla. filename,  dtupla.date_part("hour", createddate)

Alternativa per la cancellazione di record duplicati limitando la ricerca ai records
con count (*)   > 1

DELETE
 FROM downloads
 WHERE itemid NOT IN
 (SELECT MIN(dtpl.itemid)
 FROM downloads As dtpl
 GROUP BY dtpl.email, dtpl.filename, date_trunc('minute',dtpl.createddate)
 HAVING count(*) >= 1);
 SELECT 1;

Conta record che hanno alcuni campi chiave duplicati e che pertatno potrebbero essere record duplicati

SELECT *
 FROM ( SELECT email, date_trunc('hour',createddate), filename, count (filename) as totuples
 FROM contactsdownloads
 GROUP BY email, filename , date_trunc('hour',createddate)
 ORDER BY totuples DESC, date_trunc('hour',createddate) ) AS foo
 WHERE totuples > 1

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