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I want to add a unique constraint on a table, eg

ALTER TABLE report ADD UNIQUE (date, scholar_id);

Each scholar should have only one report per day and the application checks whether there is an existing report for the scholar for the date but due to having a cluster of servers I occasionally do get duplicates.

Now I need to remove aproximately 700 items from the table.

I run a query like

SELECT date, scholar_id, count(*) 
FROM report 
GROUP BY date, scholar_id
HAVING count(*) > 1;

And see about 548 rows. Some with counts = 3 or 4, most with count = 2.

These "duplicates" cause the ALTER TABLE to fail.

I am hoping to automate deleting these duplicates (all except 1 per scholar_id/date pair).

I imagine some way to get the pairs, and then per pair get all the rowids, and then DELETE FROM report WHERE id = any(...) AND NOT id = any(... limit 1);

Note: it is not important which one of the copies are removed. There are other columns and the other columns might not have identical values.

How to do this is the question...

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