PostgreSQL - aggregating data by date from datetime field -

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i have data on time particular users , timestamp of form 2013-11-23 16:00:00-05 - there's minute minute date each user , corresponding usage value.

so table has values: user_id, localminute, usage.

i trying aggregate usage @ day wise level, did far below s looking easier way without creating dummy column date_event:

alter table tablename add column date_event date update table set date_event = date(localminute) select sum(use), date_event tablename group date_event

my question how can extract date timestamp , aggregate in single query. help!

just cast date:

select sum(use), localminute::date  tablename  group localminute::date;

or using standard sql:

select sum(use), cast(localminute date)  tablename  group cast(localminute date);

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