DATE_TRUNC is played on the db where the timestamp are stored in utc.
So if a user search for 12/12/2012 in Paris timezone and that we truncate it should do something similar to :
SELECT DATE_TRUNC('day', foo.timezone) from (SELECT timestamp '2012-12-12 00:00:00' AT TIME ZONE 'Europe/Paris') as foo;
=> 2012-12-11
To avoid such pb, I suggest avoiding DATE_TRUNC when exact results are needed
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